Queensland Geological Record 2008/04

QUEENSLAND GEOLOGICAL RECORD 2008/04

Diamonds, diamond indicator minerals and a review of exploration for diamonds in Queensland

L C Cranfield & G Diprose

Queensland the Smart State ADDRESS FOR CORRESPONDENCE:

Geological Survey of Queensland Department of Mines and Energy Block A, 80 Meiers Road, Indooroopilly, QLD 4068 Telephone: (07) 3362 9364; International +61 7 3362 9364 Facsimile: (07) 3362 9343; International +61 7 3362 9343 Internet: www.dme.qld.gov.au

REFERENCE: CRANFIELD, L.C. & DIPROSE, G., 2008: Diamonds, diamond indicator minerals and a review of exploration for diamonds in Queensland. Queensland Geological Record 2008/04. i

CONTENTS SUMMARY...... 1 INTRODUCTION ...... 2 PROPERTIES AND USES OF DIAMONDS...... 3 ORIGIN OF DIAMOND...... 5 AGE OF DIAMONDS...... 5 CARBON SOURCES ...... 6 CARBON ISOTOPIC COMPOSITION OF DIAMONDS ...... 6 DIAMOND OCCURRENCES AND EXPLORATION TECHNIQUES ...... 11 HISTORICAL DIAMOND MINING IN AUSTRALIA...... 14 NEW SOUTH WALES ...... 14 VICTORIA ...... 14 TASMANIA ...... 15 SOUTH AUSTRALIA...... 15 WESTERN AUSTRALIA ...... 15 NORTHERN TERRITORY ...... 16 QUEENSLAND...... 16 DISTRIBUTION OF DIAMONDS AND INDICATOR MINERALS IN QUEENSLAND ...... 17 EXPLORATION FOR DIAMONDS IN QUEENSLAND 1960–2008 ...... 28 NORTH-WEST QUEENSLAND ...... 28 COEN AREA...... 41 LAURA AREA ...... 44 PALMER RIVER AREA...... 45 COOKTOWN AREA ...... 47 ATHERTON TABLELAND ...... 51 CROYDON AREA ...... 56 GEORGETOWN AREA ...... 59 MOUNT SURPRISE AREA ...... 60 GREENVALE AREA ...... 65 RICHMOND–HUGHENDEN AREA ...... 67 WINTON AREA ...... 67 BOULIA AREA...... 68 BEDOURIE AREA ...... 68 DIRRANBANDI AREA ...... 68 ROLLESTON AREA ...... 70 MOUNT COOLON AREA ...... 70 CLERMONT AREA ...... 71 ANAKIE AREA ...... 72 PROSTON AREA ...... 72 PITTSWORTH AREA ...... 74 STANTHORPE AREA ...... 75 CONCLUSIONS ...... 75 ACKNOWLEDGEMENTS...... 75 BIBLIOGRAPHY ...... 76 TABLE 1. World wide occurrences of diamond-bearing host rocks with known age dates ...... 7 FIGURE 1. Garnet compositions in diamond occurrences by origin ...... 6 2. Carbon isotopic composition in diamondiferous rocks ...... 8 3. Subduction origin for diamonds ...... 9 4. Schematic cross-section of a kimberlite pipe ...... 10 5. The 57 open file mineral exploration permits EPMs) that contain diamond exploration ....18 6. The number of microdiamonds found at each location ...... 19 7. The location of diamond indicator minerals found in Queensland ...... 20 8. The number of chromite grains found at each location ...... 21 9. The number of pyrope grains found at each location...... 22 10. The number of garnet grains found at each location ...... 23 ii

11. The number of picro ilmenite grains found at each location ...... 24 12. The number of chrome diopside grains found at each location ...... 25 13. Niobium (Nb) concentrations in ppm...... 26 14. The location of grains that underwent microprobe analysis...... 27 Queensland Geological Record 2008/04 1

SUMMARY

Exploration for diamonds in Queensland has continued to be influenced by the South African approach, modified by the discovery of diamonds in lamproite in Western Australia. This approach is to explore for kimberlite and lamproite bodies using indicator minerals that are dispersed from these rocks by fluvial and colluvial processes.

Exploration for diamonds in Australia has increased since the discovery and exploitation of the Argyle Mine in Western Australia. The New South Wales Geological Survey has produced a digital data product on the prospects for diamond exploration in that State as have the Northern Territory Geological Survey (as a grouping of Microsoft Excel spreadsheets with data on diamond indicator minerals) and the Geological Branch of PIRSA in South Australia. As part of the Smart Mining Initiative (2006–2010), the Geological Survey of Queensland has compiled a database of micro-diamonds and diamond indicator minerals from open file company data in the Department of Mines and Energy’s QDEX system. Much of the exploration for diamonds in Queensland has been patchy and has proceeded along with exploration for other commodities. There has been no commercial exploitation of diamonds in Queensland and only rare occurrences of microdiamonds have been reported.

This report also outlines the properties of diamonds and geological models for their formation. There appears to be a regional difference in diamond occurrences in Queensland, with the kimberlite and lamproite models favoured for the north-western regions of the State and the subduction (S-type model) favoured for the eastern coastal and sub-coastal zones, linked to Cainozoic alkalic basalt volcanism. Sapphire is commonly associated with diamonds in these areas. Studies in New South Wales indicate that diamonds do occur in economic quantities in alkali basaltic intrusions and further exploration in Queensland is warranted on diamond indicator minerals and their composition.

The main occurrences of microdiamonds have been in the Mount Isa region, where they have been reported from stream sediment samples. Microdiamonds have been found in the Stanthorpe, Proston, Herberton and Lakeland Downs areas of eastern Queensland.

Keywords: Diamonds, diamonds indicator minerals, diamond indicator mineral spreadsheets, macrodiamonds. microdiamonds, diamond exploration, exploration techniques, properties and uses of diamonds, origin of diamonds, age of diamonds, potassic-ultramafic, kimberlite, serpentine,xenoliths, lherzolite, picroilmenite, titanium- and magnesium-rich chromite, chrome diopside, magnesium-rich olivine, pyrope and eclogitic garnets, mineral geochemistry, niobium, phosphorous, nickel, chromium, peridotite, P-type, eclogite, E-type, lamproite , carbon isotopes, light rare earth elements, Archaen, Tertiary, basalt, subduction, aeromagnetic surveys, ground magnetic surveys, diamond mining, air photo interpretation, electromagnetic surveys, northwest Queensland, Coen, Laura, Palmer River, Cooktown, Atherton tableland, Croydon, Georgetown, Mount Surprise, Greenvale, Richmond-Hughenden, Winton, Boulia, Bedourie, 2 Cranfield & Diprose

Dirranbandi, Rolleston, Mount Coolon, Clermont, Anakie, Proston, Brigooda, Pittsworth, Stanthorpe, Queensland.

INTRODUCTION

Based on the popularity of the Northern Territory’s Diamond Mineral Indicator database, a similar database was constructed for Queensland. This Diamond Indicator Mineral and Geochemistry database was created to provide an overview of where diamonds and diamond indicator minerals have been found throughout Queensland. Data was extracted by the Geological Survey of Queensland from company reports held in the Departmental QDEX system, which includes reports mentioning diamond exploration as far back as 1968.

The data from these reports was extracted and entered in the diamond database. Of the 220 company reports initially extracted from QDEX, some did not contain information on diamond exploration but were selected by the query used due to mentions of ‘diamond’ in relation to drilling. In addition, some reports only contained information on magnetic, EM, gravity and other geophysical surveys carried out in relation to diamond exploration; the results of these surveys were not entered, as the focus of this database was on the indicator minerals. Only 73 company reports covering 57 separate exploration tenements contained data relevant to the database.

The Diamond Indicator Mineral and Geochemistry database is made up of three Microsoft Excel spreadsheets. Each spreadsheet concentrates on different aspects of diamond exploration.

The first spreadsheet contains data on the number and size of micro and macro diamonds located in exploration samples. The second spreadsheet contains data on the number of grains of different indicator minerals found in each sample and specific geochemical information on elements that are associated with diamond exploration. Both spreadsheets contain information such as sample number, prospect details (company, tenement information), 1:250 000 map sheet name and code, MGA co-ordinates, open file status, 1:100 000 map sheet name and code, geological region, location accuracy, sample type (for example, soil, grab, drill, etcetera), sample weight, sampling mesh size and comments. The diamond spreadsheet contains information on the number of macro and micro diamonds found in the sample and any further details of the diamond such as size, shape and weight. The diamond indicator mineral spreadsheet contains data on the quantity of indicator minerals located in each sample. Indicator minerals identified in the exploration include chromite, pyrope garnets, picroilmenite, chrome diopside and other garnets. Elements that were specifically analysed in diamond exploration and are recorded in this spreadsheet include niobium (Nb), chromium (Cr), nickel (Ni), cobalt (Co) and titanium (Ti).

The third spreadsheet summarises the analysis of indicator minerals and compares their composition with that expected for diamondiferous erosion products derived from a kimberlite origin. In general, analyses were carried out by electron microprobe. The data contained in this spreadsheet includes sample number, grain Queensland Geological Record 2008/04 3 number, type of mineral, source of data, company, tenement details, open file status, MGA co-ordinates, analysis results for SiO2,TiO2,Al2O3,Cr2O3,Fe2O3, V2O3,FeO,MnO,MgO,ZnO,NiO,Na2O, K2O, ZrO2,SO3,Nb2O5, CaO and P2O5, total percentage and comments. The information gathered from the composition analysis is used to determine whether the grain has a composition similar to that expected from a grain of kimberlitic origin.

The diamond database summarises critical data relating to previous diamond exploration in Queensland. The data can be viewed in ways that allow the identification of areas that would benefit from further exploration.

There are four main areas where diamonds and indicator minerals have been found — north-west Queensland, central western Queensland, south-east Queensland and northern Queensland.

PROPERTIES AND USES OF DIAMONDS

Three hallmarks of true gems are beauty, durability and rarity. Diamond is by far the hardest natural substance and therefore more durable than other gemstones. Diamond is the high pressure form of pure carbon. It is singularly refracting and has a refractive index of 2.417, a dispersion of 0.44, a Mohs’ scale of hardness of 10 and a density of 3.52. It has a perfect octahedral cleavage in four set and a conchoidal fracture. Colour is variable from colourless to red and includes yellow, brown, blue, pink and even violet. Intense pink diamonds (possibly indicating high pressure for time periods up to 3Ga) are currently the most valuable variety and 95% of these come from the Argyle Mine in the north-east of Western Australia.

Lustre in diamonds can vary from adamantine to greasy or occasionally dull. Gem quality diamonds are required to be transparent whereas industrial diamonds can vary from translucent to opaque. Many diamonds are isotropic, but some exhibit a double refraction attributable to internal strain that is most noticeable in proximity to cavities and inclusions. Diamonds most commonly occur as isolated crystals in the form of a perfect octahedron, an octahedron with curved faces, an icositetrahedron or hexoctahedron, a rhombic dodecahedron or tetrahexahedron with rounded corners and slightly curved faces, or an almost spherical shape. Curved faces are commonly striated and may exhibit triangular markings in the form of shallow pits. Flattened triangular twinned forms are also found. Cubic forms are rare.

Diamond can also form as spherical masses of minute, intergrown crystals, arranged more or less concentrically. This material has a generally irregular or globular appearance and is called ballas. Another microcrystalline form occurs as massive, impure, cellular crystal aggregates forming a granular to compact structure. Colour may be black, brown or dark grey. This material is referred to as carbonado. The lowest quality diamond is called bort. Hailstone bort is a rounded form that differs greatly in appearance and structure from other forms. Typically, it consists of alternating layers of grey to clear, poorly to well-crystallised minute diamond crystals. Framesite is a coarse, gritty, rather friable variety of bort 4 Cranfield & Diprose showing minute brilliant points. This material is found mainly in the Premier Mine in South Africa. Stewartite is another form of bort. This rare type has a cinder-like structure with a dull sheen and occurs in shapeless lumps. It is magnetic and polar due to magnetite and silica impurities. Ballas, carbonado and bort are used only for industrial purposes.

Theoretically diamond is pure carbon and colourless. In common with other natural substances, diamond can contain imperfections of one kind or another. Based on these imperfections diamonds can be subdivided into four main types and one subsidiary type:

• Type 1A contains up to 0.2wt% nitrogen, which appears to be segregated into relatively large sheets of platelets within the crystal (99% of all type 1 diamonds)

• Type 1B is similar to type 1A , but nitrogen is more dispersed and takes the place of carbon in the crystal lattice (0.1% of type 1 diamonds)

• Type 2A is relatively free of nitrogen. Type 2 diamonds do not fluoresce when irradiated by ultraviolet light emitted by a high pressure mercury lamp fitted with a nickel oxide filter. These diamonds have enhanced optical and thermal properties and are rare in nature.

• Type 2B is a very pure type of diamond that has semi-conductive properties and is highly sensitive to pressure changes. Crystals are generally blue in colour and very rare.

• Type 3 includes diamond found in meteorites (lonsdaleite) and meteorite craters. It has been synthesised from graphite in the laboratory.

Diamonds are inert, resist all forms of acid and have an extremely high thermal conductivity. They are non-metallic and generally do not conduct electricity. They have a higher resistance to abrasion than any other natural materials and have a high bulk compressive stress and elastic modulus. Diamonds are completely transparent to a broad segment of the electromagnetic spectrum, which makes them useful in industrial, technological and scientific applications

Diamonds are used in the jewellery industry and are also are used for machining plastic, glass and metal pieces necessary in products such as laser printer drums, polygon mirrors, automobile engine pistons, telephone, television, computers, and CD players.

Diamonds can be made into ultra-hard and smooth cutting knifes and scalpels for extremely precise surgery. Their resistance to wear becomes an asset in automated processes that need to make large number of copies of a same product, without having to replace the cutting tool. Diamonds also form part of dental drills. Their hardness also makes them useful as abrasive and grinding material. Queensland Geological Record 2008/04 5

ORIGIN OF DIAMOND

Diamonds typically occur in kimberlite and lamproite. Kimberlite is a ‘hybrid’ rock composed of fragments of peridotite and eclogite derived from the upper mantle, as well as fragments of various rock types derived from higher levels in the crust. These fragments are contained in a finer matrix composed of crushed and disaggregated fragments and crystallized minerals from a potassic-ultramafic (kimberlite) magma. Chemically, kimberlite is an ultramafic rock with high potassium, water, and carbon dioxide. The high potassium levels may result in the formation of phlogopite mica, the carbon dioxide may result in the formation of calcite, and the high water may result in the formation of hydrated minerals such as serpentine. At the surface, kimberlite weathers to a rubbly yellow-brown rock. Fresh kimberlite is harder and is commonly grey in colour (Cannon & Murdrey, 1981). Although diamond crystals are found in kimberlite and related rocks, the apparent origin of diamond is more closely related to the fragments of peridotite or eclogite which are derived from the upper mantle below cratonic (shield) areas. In order for diamonds to form, they require extremely high pressures and temperatures, which are only found in these deep levels of the earth. At these depths, eclogite is formed, consisting of red pyrope garnet, green clinopyroxene and locally diamond crystals.

Peridotite fragments (xenoliths) comprising garnet, olivine and orthopyroxene also contain diamonds and are similarly derived from the upper mantle. However, these fragments commonly disaggregate during the emplacement process resulting in a matrix containing disaggregated olivine, pyroxene and diamond as xenocrysts.

As diamonds have a close affinity to the type of xenolith (eclogite, peridotite) and their respective source areas, they can be subdivided into those which have a peridotitic origin (P-type) and those which have an eclogitic origin (E-type). Even though a diamond may be found as a xenocryst (single crystal) within the kimberlite matrix, inclusions or flaws within the diamond crystal can identify its origins. These flaws or inclusions can consist of associated minerals such as garnet, pyroxene, olivine, chromite and sulphides (pyrrhotite). The chemistry of the mineral inclusion can be compared with that of minerals present in the eclogite and peridotite fragments to determine their source. Inclusions also provide valuable information that allows the determination of formation pressure, temperature and age. Figure 1 shows the chemical composition fields for peridotite, eclogite and lamproite-derived garnets.

AGE OF DIAMONDS

By analysing inclusions in diamonds such as pyroxene and garnet, which contain measurable quantities of radioactive elements (U/Pb), it is possible to establish a radiometric age for the inclusion and by extension for the diamond containing it. Similarly, radiometric age dates can be established for the minerals that crystallized during emplacement of the kimberlite host rock. Comparing the ages of diamonds with those of the host rocks shows that diamond crystals commonly pre-date their age of emplacement in the containing rock body. In many cases, 6 Cranfield & Diprose Ca Ca

Eclogitic Garnet

Peridotitic Garnet

Lamproite Garnet Mg Fe 08B/LC-10-08/fig1.cdr Figure 1: Garnet compositions in diamond occurrences by origin diamond crystals have been resident in the upper mantle for billions of years prior to their more recent emplacement. This geochronological evidence supports the view that diamonds are formed in the upper mantle of the earth and do not crystallize as part of a kimberlite ‘magma’ as once had been believed. Table 1 shows the variation of host rock and enclosing xenoliths in diamonds.

CARBON SOURCES

The classification of diamond crystals based on peridotitic (P-type) and eclogitic (E-type) host source rocks is also reflected in the carbon isotopic composition of the diamond. Carbon has isotopic characteristics that can guide us in determining the source of the carbon and as such provide some insight into how the diamond and its source rock formed.

CARBON ISOTOPIC COMPOSITION OF DIAMONDS

Carbon isotopic studies measure the ratio of 13Cto12C (expressed as ä13C). These carbon isotopic ratios indicate that diamonds of a peridotitic origin have a smaller range (-10 to 0) than diamonds of an eclogitic origin (+3 to -34) (Kirkley & others, 1991).

This difference is related to the different origins for these rocks and their contained carbon. Eclogite is thought to form as the residue from partial melting of a subducting oceanic slab that contains rocks with a wider range of carbon isotopic values. Here, carbon may be derived from near-surface carbonates and hydrocarbons. In contrast, peridotitic diamonds have carbon isotopes that have not been significantly fractionated (smaller range) and are probably derived from a more homogeneous source representing original constituents of the primitive mantle of the earth. Queensland Geological Record 2008/04 7

Table 1: World wide occurrences of diamond-bearing host rocks with known age dates

Location (Mine) Rock Type Mined Age of Host Age Type of Reference Diamond (Ma) Inclusion (Ma) Kimberley, Kimberlite Yes ~3300 ~100 Peridotitic Kirkley & others South Africa (1991) Finsch, South Kimberlite Yes ~3300 ~100 Peridotitic Kirkley & others Africa (1991) Finsch, South Kimberlite Yes 1580 ~100 Eclogitic Kirkley & others Africa (1991) Premier, South Kimberlite Yes 1150 1100– Eclogitic Kirkley & others Africa 1200 (1991) Argyle, Western Lamproite Yes 1580 1100– Eclogitic Kirkley & others Australia 1200 (1991) Orapa, Botswana Kimberlite Yes 990 ~100 Eclogitic Kirkley & others (1991) United States of Olivine leucite Yes N.A. Eclogitic America Tasmania Peridotite No China Peridotite Yes N.A. Garnet Xu Shutong & Eclogite, garnet others (1992) pyroxenite and jadeite Morocco Garnet No N.A. - Graphitic Pearson & others pyroxenite pseudomorphs (1989) Ural Mountains Picrite No N.A. Russia Syria Basanite No N.A. Jugiong, New Nephelinite No N.A. South Wales Sydney Basin Alkali Basalt No 300 0.46 Eclogitic diatremes, Inverell Alkali Basalt Yes volcaniclastics (Copeton, New South Wales Brigooda, Alkali basalt No Queensland Africa Diabase No N.A. (dolerite) Kazakhstan Gneiss No N.A. Meteorites Various No N.A. Anders & Zinner (1993) China (Central Eclogite, No N.A. 500–1800 Eclogitic and Yang & others Orogenic Belt) Felsic gneiss felsic gneisses as (2003) inclusions in zircon Norway Megacrystic No N.A. - Inclusions in Dobrzhinetskaya garnet websterite garnet & others (1995) Japan Lamprophyre No N.A. 17.7±0.5 Peridotitic Mizukami & others (2008) 8 Cranfield & Diprose

100 Peridotitic Diamonds

n Eclogitic 50 Diamonds

08B/LC-10-08/fig2.cdr -40 -30 -20 -10 0

Figure 2: Carbon isotopic composition in diamondiferous rocks (after Kirkley & others, 1991) The subduction origin of diamonds was proposed to explain the creation of eclogite as a residue from partial melting of subducting oceanic slab (modified after Kirkley & others, 1991). This model has been proposed for diamond occurrences in New South Wales (Barrows & others, 1996) and China (Yang & others, 2003). Recently, diamond was discovered for the first time in a forearc environment (microdiamonds in zircons in a lamprophyre dyke in forearc sediments) in Japan (Mizukami & others, 2008).

Eastern New South Wales has produced more than 500 000 carats of diamonds, mainly from the Copeton–Bingara area (Barrows & others, 1996). These authors assume a local origin for the diamonds because of their distinct tribal character, lack of surface damage, and the fact that their carbon isotopic values and mineral inclusions are unlike those in diamonds from conventional diamond-producing areas in Siberia, South Africa and Western Australia. Barrows & others (1996) proposed that prolonged Phanerozoic subduction of mature oceanic crust resulted in the development of a low-temperature metamorphic window into the diamond Queensland Geological Record 2008/04 9

Craton

Sedimentary Rocks Subduction Continental Crust Oceanic Crust Zone Mantle Mantle (Solid) (Solid)

Mantle Mantle (Partially Molten) (partially Molten)

0 100 Kilometres

08B/LC-10-08/fig3.cdr

Figure 3: Subduction origin for diamonds stability field within the down-going slab at half the depth required by conventional models. Diamonds are considered to be preserved by termination of subduction, and then brought to the surface by obduction or by entrainment in suitable magmas. The type of diamond formed depends on the original source rock, for example carbonaceous-rich and carbonaceous-poor trench sediments (Ca-Fe-Mg-Mn silicate, eclogitic), graphite-poor basalt and gabbro (eclogitic) and lherzolite (peridotitic). Barrows & others’ model predicts that the diamonds in the eastern coastal zone are Phanerozoic in age and that their features, associated minerals and geographic distribution relate to New South Wales tectonic provinces. They proposed that additional indicator minerals such as macro-diamond, corundum and Na-garnet be evaluated in a search for these deposits and that a greater range of magmas be considered as hosts (for example, basanite, nephelinite, leucitite). They also suggested that the diamond potential of eastern New South Wales needed to be re-evaluated in terms of their model. Diamonds and corundum in central Queensland are also thought to be sourced from spatially associated Tertiary basaltic pyroclastic rocks, and again diamonds may be somewhat earlier in age than the sapphires (Robertson & Sutherland, 1992). The occurrence of a microdiamond at Brigooda in eastern Queensland indicates an origin in Tertiary volcanic rocks (Robertson & Robertson, 1994).

Diamond-bearing kimberlites are portions of the upper mantle that have been emplaced into shallow levels of the earth’s crust. This emplacement requires deep fractures extending below the base of the craton to the upper mantle. As these fractures tap deep levels, a combination of high pressure, high temperature and high volatile (H2OandCO2) content results in the release of a kimberlitic ‘magmatic fluid’ from depths of at least 100km. The initial ascent is rapid, with speeds estimated in the order to 10–30kph. Within 2–3km of the surface, the velocity of the magmatic fluid increases to several hundred kilometres per hour (Kirkley & others, 1991). This rapid increase is due to a combination of low pressure and interaction with high-level groundwater, resulting in explosive brecciation of wall rocks and the formation of a kimberlite ‘pipe’. 10 Cranfield & Diprose

Figure 4: Schematic cross-section of a kimberlite pipe (modified after Kirkley & others, 1991) The explosive emplacement of the volatile-rich kimberlite magmatic fluid results in the development of a near-surface kimberlite ‘pipe’. These pipes have a ‘carrot’ shape and are several hundred metres in diameter near surface, narrowing to 1-10m at depth. They generally extend over a vertical distance of 2-3km. An idealized model of a kimberlite pipe can be subdivided into three zones: the root, diatreme and crater. The root zone is characterized by crystallized kimberlite magma with typical intrusive textures and containing xenoliths (fragments) and xenocrysts (crystals). The root zone extends into a feeder dike or fractures along which the magmatic fluid passed.

The diatreme zone is the main source of diamonds due to its larger size and significant volume of kimberlitic rock. It contains the bulk of the xenoliths derived from the mantle as well as fragments of wall rock. In this zone, there is rapid explosive expansion of the kimberlite magmatic fluid due to the contained volatiles. Following expansion, rapid cooling takes place. With only minor thermal contact metamorphic effects, the diamond crystals are able to resist conversion to graphite. As the kimberlite volcano erupts, the debris is deposited into the crater zone. Queensland Geological Record 2008/04 11

The crater zone is composed of two types of kimberlite: 1) pyroclastic kimberlite — composed of tuffs deposited on the surface and within the pipe vents, and 2) epiclastic kimberlite — composed of eroded pyroclastic kimberlite that has been redeposited either outside of or within the pipe vent. Sedimentary features such as bedding and sorting are common within the crater zone. The crater zone also contains xenoliths of surficial cover rock, vegetation (e.g. wood) and terrestrial organisms (e.g. microfossils) that existed at the time of emplacement. Although diamond crystals form in the upper mantle below cratonic areas, they can only remain stable at high pressures and temperatures. The mantle xenoliths and diamond crystals that are brought quickly to surface in a kimberlite magmatic fluid are able to survive near surface in a ‘quenched’ or ‘meta-stable’ state. If the intrusion of kimberlite is delayed during its rise to the surface or is trapped in the lower crust, diamond crystals will not be stable in the P-T environment and will revert to graphite.

Diamond crystals can remain stable at shallower depths under shield or cratonic areas due to the low geothermal gradient related to the sub-cratonic keel beneath the continental crust. This P-T environment has been referred to as the diamond ‘storage area’ (Kirkley & others, 1991). The keel area is an optimal source for diamonds since fractures below the craton are more likely to tap this area and remain accessible to the surface.

DIAMOND OCCURRENCES AND EXPLORATION TECHNIQUES

Macro diamonds are derived from diamondiferous peridotites and ecologites that formed in the lithospheric upper mantle. Diamonds are accidental xenocrysts in their kimberlite or lamproite host rocks. Diamondiferous units typically form discontinuous lenses or pockets within the upper mantle beneath stable, thick Archean cratons. There are peridotitic and eclogitic diamond occurrences. Peridotitic diamond occurrences are the more common. The paragenesis of the diamond xenocrysts is commonly significantly older than the volcanic host rock that transported the diamonds to the earth’s surface.

Peridotitic diamonds predominantly form in a chemically depleted peridotite near the base of the lithosphere at depths ranging from 150–200km and have been the result of metasomatism developed in a Ti poor, light rare earth element (LREE), K and Rb enriched event.

Eclogitic diamonds show a range of ages and most if not all are apparently younger than the oldest Archean peridotitic diamonds (990–2700Ma).

A range of parameters must be satisfied for diamonds to be preserved. Significant among these are that transport to the surface must be rapid and that the environment must be typically volatile and linked to ultrapotassic, ultrabasic volcanic activity. 12 Cranfield & Diprose

Commercial diamonds in Australia occur in lamproites (for example, Argyle). Historically, the two main rock types where commercial diamonds are found are kimberlites and lamproites.

Kimberlites form pipe-like bodies, usually in clusters. Diamond occurrences are generally within 50km of a cluster. The age of the occurrences can range from Archean to Tertiary. Occurrences in kimberlites commonly form carrot-shaped pipes, dykes and sills.

Occurrences in lamproites are variable in age range, are generally <0.5km in depth and have no root type structure. They typically form champagne glass shaped craters with shallow, irregular pipe wall contacts. The craters are generally infilled by volcaniclastic rocks dominated by primary pyroclastics (for example, lapilli tuffs).

Diamond indicator minerals identified from Scanning Electron Microscope (SEM) studies include picroilmenite, titanium- and magnesium-rich chromite, chrome diopside, magnesium-rich olivine, pyrope and eclogitic garnets. The variety and number of diamond indicator minerals apparently has no bearing on the grade of the diamond occurrences.

Garnets that have a peridotitic and eclogitic paragenesis contain moderate to high levels of TiO2, whereas lamproites often contain G5 (iron-rich) garnets.

Chromite in diamondiferous deposits contains moderate to high levels of magnesium, average chrome, and is very low in TiO2 levels. Orthopyroxene in diamond deposits is compositionally a chrome-rich diopside that generally is not preserved and is characterised by high MgO and low Al2O3 levels. Olivine specific to diamond deposits is not readily distinguishable due to the overlap of compositional fields, but its presence is significant as it is generally not preserved. Tourmaline, zircon and Nb-rich rutile have been useful indicators in exploration for lamproite in Australia. However, the overlap in composition between these minerals indicates they are not useful in other areas and that further studies are needed to develop their use in exploration.

Exploration techniques used for diamond exploration include airborne and ground geophysical methods such as magnetics, electromagnetics (EM) and gravity.

Detailed gravity surveys attempt to locate a signature that is less than the surrounding host rock in order to outline the size and shape of a pipe.

EM surveys measure electrical resistivity at or near the Earth’s surface and can locate pipes that have well-developed, weathered, conductive, clay-altered upper portions. The main characteristic of a potential target body is that it must have a good conductive contrast to the surrounding rocks.

Surface sampling involves the use of various media, but the basic premise is the delineation of the dispersion patterns for anomalous chemical elements or mineral grains and linking a dispersal trail to the source. This requires considerable knowledge of the geological history of the area, which in the Queensland context Queensland Geological Record 2008/04 13 relates to paleolandforms produced by Cainozoic volcanic or alluvial activity that has occurred since emplacement of the diamonds into a host rock.

Soil sampling methods for identifying kimberlite make use of increased levels of trace elements such as niobium, phosphorus, nickel and chromium. These elements are generally closely restricted to a few tens of metres from the pipe. Higher clay content in altered kimberlites often creates anomalous vegetation changes due to their higher water retention. These changes can be interpreted from aerial photographs.

The most common exploration technique for diamond indicator minerals is analysis of heavy mineral concentrates from bulk samples. This is the oldest and most widely used technique in diamond exploration. In Queensland, samples have mainly been collected from drainages. Resistant heavy minerals commonly associated with kimberlite structures include garnet, chromite, ilmenite, chrome diopside, olivine and picroilmenite. In addition to the composition of the grain, its appearance is important in identifying its mode of transport and the distance travelled from the source.

Early studies of diamond inclusions identified an important suite of harzburgitic minerals, especially low-Ca, high-Cr (‘G10’) pyrope garnets and high-Cr chromites. The use of this suite of ‘indicator minerals’ has led to some significant exploration successes (especially in South Africa and Siberia) but has proven misleading in several other regions, leading to a significant waste of exploration resources. It is important to look at a range of evidence from exploration to determine the likelihood for discovery of diamonds.

In the context of data mining previous company exploration in Queensland, the internal Departmental company exploration digital data report system (QDEX) was utilised to retrieve reports for tenures where the holder had carried out any exploration for diamonds or diamond indicator minerals. Each report was assessed to extract any data on diamond or diamond indicator minerals. Information extracted included diamond indicator minerals, macro and micro diamonds and detailed microprobe analysis to demonstrate the specific chemistry of diamond indicator minerals relevant to diamond exploration. Three spreadsheets were used to record the data contained in these reports. The first spreadsheet contains data on macro and micro diamonds found, the second on diamond indicator minerals, and the third spreadsheet contains data from microprobe analysis.

Exploration methods common throughout these reports include aeromagnetic surveys, ground magnetic surveys and air photo interpretation to establish any anomalies that may represent a kimberlitic pipe. Bulk samples were collected from likely areas on the surface and drilling was carried out locally to determine whether the samples contained indicator minerals. In some cases, diamond exploration was carried out in areas that had at some stage reported findings of diamonds. Other areas considered for diamond exploration were those that had a favourable geological terrane for formation of kimberlitic structures. 14 Cranfield & Diprose

Diamond indicator minerals studied usually include chromite, pyrope garnets, picroilmenite and chrome diopside. The number of grains found was counted and recorded for each mineral. In some instances, a selection of these mineral grains was sent for examination by microprobe analysis to ascertain if the mineralogy of the grain was consistent with derivation from a kimberlitic source.

Another method occasionally used was geochemical surveys to test for anomalous niobium concentrations. It is has been demonstrated that kimberlitic structures have an increased niobium concentration compared with surrounding areas. However, this is debatable as high niobium is not only restricted to kimberlitic structures and there are many different situations that would result in high niobium levels. Despite this, it has occasionally been used as a preliminary survey to assess an area before deciding on further exploration work.

HISTORICAL DIAMOND MINING IN AUSTRALIA

Diamonds were discovered in New South Wales in 1851, in Victoria in 1861, in Queensland in 1873, in South Australia in 1879, in Tasmania in 1894, in Western Australia in 1895 and in the Northern Territory in 1980.

NEW SOUTH WALES

In 1851, Edward Hargraves discovered diamond at Reedy Creek, 25km south-west of Bathurst. This was followed in the same year by a diamond discovery at Burrendong, 70km north of Bathurst and, in 1860, by further discoveries by gold prospectors in the Macquarie River. The first significant discovery came from a deep lead worked for gold near the junction of the Cudgegong River and Reedy Creek, which produced 3000 diamonds in two years.

Another deep lead near Bingara produced a rush and was worked intermittently up until 1904 producing 33 836ct of diamonds, of which 15 000ct were recovered in 1894. Diamond was found in alluvium at Copes Creek (Copeton) in 1875 and later traced to deep leads under basalt. Most of the diamond from this deposit was recovered between 1876 and 1922. Eastern New South Wales has produced more than 500 000ct of diamonds, mostly from the Copeton–Bingara area (Barrows & others, 1996).

VICTORIA

Diamond was first discovered in Victoria near Beechworth in the Woolshed Valley. Diamonds less than 1 carat have been found at Wooragee, the lower end of Reid’s Creek, the Woolshed, Sevastopol and Eldorado. The stones ranged in colour from a yellowish tint to colourless and commonly formed modified trisoctahedra. Since 1861, several hundred good quality stones have been recovered during alluvial gold mining. Larger stones included a 5ct stone from Wooregeeup and a 17.64ct stone from the Woolshed Valley area. Queensland Geological Record 2008/04 15

TASMANIA

Diamonds have been known from Tasmania since 1894, when they were first found in the north-west by L. Harvey, a prospector sluicing for gold, reportedly in Sunday Creek and Harveys Creek, both of which have been described as tributaries of the Savage River (Bottrill, 1998). Diamonds were discovered in the Donaldson River–Savage River area, including Middletons Creek and possibly Badger Creek (now Savage Creek), but the exact locations are uncertain. Official records indicate only 16 or 18 discoveries were authenticated up to 1910. Reid (1921) reported the presence of diamonds in thin-sections of peridotite from the Heazlewood Ultramafic Complex at Bald Hill, north-east of Savage River. This reportedly occurred in olivine, within and predating chromite, but was not confirmed by later studies. There have been more recent verbal reports of some diamonds being found in the Corinna district, but there is no evidence that these have been verified.

SOUTH AUSTRALIA

In 1879, the Commissioner of Crown Lands engaged Mr G.T. Bean, an experienced gem digger, to examine and report on the Echunga field. Bean reported diamonds from several localities and that Chapman’s Gully looked very much like the diamond fields of the Kimberley in South Africa. Bean also recommended that a systematic search should be undertaken. Since then, most diamonds found in that area have been accidental discoveries while panning for gold.

At Mount Kingston in the far north of South Australia, a diamond was discovered in 1894 by a small party looking for gold. Another diamond was discovered at Algebuckina, in the same area, in 1908. Others have been found at Edwards Creek, ~100km south of Oodnadatta.

WESTERN AUSTRALIA

Alluvial diamonds were discovered at Nullagine, in the Pilbara region of Western Australia, by gold prospectors in 1895 (Groom, 1896; Simpson, 1952). Systematic exploration of that area did not begin in earnest until 1965. In 1967, attention focused on the West Kimberley region where the geological setting and previous work elsewhere in the world had suggested good exploration prospects (Clifford, 1966; Deakin & others., 1989). Lamproites in the West Kimberley were first studied in the 1930s and their relationship to kimberlites was recognised (Wade & Prider, 1940). Until the 1960s, kimberlites were thought to be the only primary source of diamonds at the surface of the Earth. Prider (1960) suggested the possibility that lamproite may also be diamond-bearing. From 1967 to 1971, diamond exploration intensified in Western Australia but was mainly confined to a very few companies that extended their search area into the Kimberley region. In 1973, the Kalumburu joint venture discovered a diamond in the King George River region. In 1976, several large diamondiferous lamproite pipes were discovered at Ellendale in the West Kimberley region. Argyle was discovered in 16 Cranfield & Diprose

1979. Production from the AK1 pipe at Argyle and the alluvials along Smoke Creek comprises about 40% of the world recorded production for diamonds, but only about 6% by value due to the high percentage of industrial diamonds (Fetherston & Searston, 2004).

NORTHERN TERRITORY

Prior to the 1970s, the only recorded diamond exploration was by Stockdale Exploration, which discovered a microdiamond near Alice Springs. Since this time, exploration has delineated a zone of microdiamonds extending from the Victoria River region into Queensland north of Mount Isa. Exploration in the McArthur Basin has led to the discovery of kimberlitic rocks (Emu Pipes) containing diamonds. The Coanjula Pipes are of unusual composition and can be described as kimberlitic. They contain crustal xenoliths and xenocrysts and their whole rock geochemistry is highly variable. No economic concentrations are known. Some of the distribution of the diamonds from this field into Queensland is apparently by wind action (Lee & others, 1994).

QUEENSLAND

Diamonds have been recovered during tin mining operations around Stanthorpe and in north Queensland and during sapphire mining in the central Queensland gemfields.

The diamonds in the Stanthorpe area were generally <1ct, although stones greater than this have been reported. In 1872, a 3.5ct diamond was reported to have been found and newspaper reports indicated that more than 100 diamonds were recovered. This news prompted John Moffat and party to set up a diamond saving machine on Spring Creek in 1873. The machine (manufactured by Smellie and company of Brisbane) recovered only three or four diamonds in eight months before being transferred to Kettle Swamp.

One hundred to 150 small diamonds have been recovered during tin mining in the Mount Surprise district since 1970. The largest diamond reported (unconfirmed) was 5ct in weight. In the Herberton area the Herberton Deep Lead extends from Herberton to Prairie Creek on the southern margin of the Atherton 1:100 000 Sheet, and south for a further 26km into the Mount Garnet 1:50 000 Sheet, to the junction of the Millstream and the Wild River. Cassiterite in the deep lead occurs with small quantities of ilmenite, wolframite, topaz, gold and rare diamonds accompany the cassiterite (Blake, 1972). One of these diamonds (0.166 carats) was confirmed by Stockdale Prospecting as being a yellow brown rounded dodecahedron which has had a vigorous and lengthy transportation; brown spots indicate a thermal event.

Diamonds have been recovered as a by-product of sapphire mining in the central Queensland sapphire fields since the early 1900s. These discoveries have not been officially reported, but there are unconfirmed reports of diamonds >5ct being recovered. Queensland Geological Record 2008/04 17

Since 1984 prospecting and exploration in the Mount Isa Inlier has uncovered the presence of microdiamonds.

DISTRIBUTION OF DIAMONDS AND INDICATOR MINERALS IN QUEENSLAND

To date there are essentially two main areas in Queensland in which most diamond exploration has been undertaken. These are north-western Queensland (the Mount Isa area) and inland northern Queensland (covering an area from Charters Towers through to Coen). Fifty-seven mineral exploration permits have produced extractable data on diamond exploration.

There were 2037 samples containing diamond indicator minerals. Of these, 1232 only looked at niobium concentration and went no further. There were 463 samples where microdiamonds were found but no macrodiamonds were reported, although many reports mention that diamonds had been found previously by prospectors and were often the reason for the initial diamond exploration. Weight, size and colour of the diamonds have been recorded where available. The larger stones recorded were from EPM 3907 and were 3.28mm by 3.0mm by 2.2mm, 3.74mm by 2.8mm by 1.6mm, 3.5mm by 2.75mm by 2.1mm, 3.4mm by 3.0mm by 2.0mm, 3.3mm by 2.8mm by 2.5mm and 3mm by 2.8mm by 2.8mm. Reports for 15 exploration permits included the results of indicator mineral analysis using microprobe analysis of specific grains. These analyses were carried out on a total of 896 grains.

To date, diamond exploration in Queensland has been unsuccessful in delineating a commercial operation. The reporting indicates that there were a range of different reasons for discontinuing diamond exploration even when micro diamonds and indicator minerals had been located. This is probably due to the perception that the diamonds were not of local origin. In many instances, the exploration effort for diamond was minor, often forming a side project to other exploration programs. In other areas when indicator minerals had been found, it was decided that these were not related to a kimberlitic source, without further analysis. Commonly, it was decided that the results were not promising enough to spend further money on the exploration project.

Figure 5 shows the 57 mineral exploration permits that contained diamond exploration data. A summary of the diamond exploration carried out in each of these permits by region is given in the next section of this report.

Figure 6 shows the number of microdiamonds found at each location. Figure 7 shows the location of diamond indicator minerals found in Queensland. Figure 8 shows the number of chromite grains found at each location. Note the high concentrations of chromite grains in the Proston region of south-east Queensland.

Figure 9 shows the number of pyrope grains found at each location. Note the high levels of concentration of pyrope garnet in the Mount Surprise area of northern Queensland and the Proston area of south-east Queensland. 18 Cranfield & Diprose

9° Queensland Geology showing EPMs that contained Diamonds and Diamond Indicator Minerals

EPM Boundary 10° Great Australian Basin Georgina Basin Carpentaria Basin Barnard Province EPP Boundary Late Carboniferous - Triassic Intracratonic Basins Cape River Province Late Devonian - Late Carboniferous Anakie Province Intracratonic Basins

NEOPROTEROZOIC - Gympie Province EARLY PALAEOZOIC Iron Range Province Connors-Auburn Province Croydon Province 12° Texas Province Savannah Province Wandilla Province South Nicholson Basin Silverwood Province McArthur Basin Yarrol Province Etheridge Province Broken River Province Eastern Fold Belt Province

TASMAN OROGENIC ZONE 14° Hodgkinson Province Western Fold Belt Province

Coen PROTEROZOIC SHIELD Fork Lagoons Province Kalkadoon-Ewen Province Thalanga Province Murphy Province

Laura Geological boundary Cooktown Approximate geological boundaries of Carpentaria, 16° Palmer River Eromanga, Surat and Clarence-Moreton Basins Subsurface geological boundaries of Late Carboniferous to Triassic Basins Subsurface geological boundaries of Early Devonian to Early Carboniferous Basins Atherton

18° Croydon 0 100 200 300 400 Georgetown Mount Surprise Kilometres Greenvale

20°

Richmond Hughenden Mount Coolon

22° Winton

Boulia Croydon Clermont

24° Anakie Bedourie Rolleston

26°

Proston

28° Pittsworth

Dirranbandi Stanthorpe

30° 138° 140° 142° 144° 146° 148° 150° 152° 154° 08A/GD-01-08/figure5.cdr Figure 5. Figure 5: The 57 open file mineral exploration permits (EPMs) that contain diamond exploration data Queensland Geological Record 2008/04 19

9° MICRODIAMONDS MICRODIAMOND GRAINS

! 1 ! 10° 2 Great Australian Basin Georgina Basin ! 3 Carpentaria Basin Barnard Province Late Carboniferous - Triassic ! Intracratonic Basins Cape River Province 4 Late Devonian - Late Carboniferous Anakie Province ! Intracratonic Basins

NEOPROTEROZOIC - 5 Gympie Province EARLY PALAEOZOIC Iron Range Province ! Connors-Auburn Province Croydon Province 12° 6 Texas Province Savannah Province ! 7 Wandilla Province South Nicholson Basin ! 8 Silverwood Province McArthur Basin Yarrol Province Etheridge Province ! 11 Broken River Province Eastern Fold Belt Province

TASMAN OROGENIC ZONE 14° Hodgkinson Province Western Fold Belt Province

Coen PROTEROZOIC SHIELD Fork Lagoons Province Kalkadoon-Ewen Province Thalanga Province Murphy Province

Laura Geological boundary Cooktown Approximate geological boundaries of Carpentaria, 16° Palmer River ! Eromanga, Surat and Clarence-Moreton Basins Subsurface geological boundaries of Late Carboniferous to Triassic Basins !! ! ! Subsurface geological boundaries of Early Devonian to Early Carboniferous Basins Atherton

18° Croydon Mount 0 100 200 300 400 Georgetown Surprise Kilometres ! !! ! !!!!!!!! ! !!!!!!!!!!!!!!! Greenvale ! ! !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!!! ! ! !!!! ! ! !!!! ! !!!!!!!!!!!!!!!!!!!!!! !!!!!! !!!!!!!!!! !! !!!! ! !! !! !!! !! 20° ! ! !! ! !!! Richmond Hughenden Mount Coolon

22° Winton

Clermont Boulia Croydon

24° Anakie Bedourie Rolleston

26°

Proston

28° Pittsworth

Dirranbandi Stanthorpe

30°

138° 140° 142° 144° 146° 148° 150° 152° 154° 08A/GD-01-08/figure6.cdr Figure 6. Figure 6: The number of microdiamonds found at each location 20 Cranfield & Diprose

9° DIAMOND INDICATOR MINERALS

! INDICATOR MINERALS

10° Great Australian Basin Georgina Basin Carpentaria Basin Barnard Province Late Carboniferous - Triassic Intracratonic Basins Cape River Province Late Devonian - Late Carboniferous Anakie Province Intracratonic Basins

TASMAN OROGENIC ZONE 14° Coen Hodgkinson Province Western Fold Belt Province !! !!! PROTEROZOIC SHIELD !!!!!! !!!! !!!!!!!!!!!! !!!!!!!!!! !!!!!!!!!!!!!!!! Kalkadoon-Ewen Province !!!!!!!! !!! Fork Lagoons Province !!!!!!!!!!!!!!!!! !!!!! Thalanga Province Murphy Province

Laura Geological boundary ! Cooktown Approximate geological boundaries of Carpentaria, Palmer River !!!!!!! !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! 16° !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! Eromanga, Surat and Clarence-Moreton Basins Subsurface geological boundaries of Late ! !! Carboniferous to Triassic Basins ! ! !!!! ! !! ! !! ! Subsurface geological boundaries of Early Devonian !! ! ! !!!!!! to Early Carboniferous Basins ! ! ! ! !! ! !!!!!! Atherton !!!!!! ! !! !! !! !! !! ! ! !!!!!!! ! !!!!! ! !!! !! ! ! ! ! ! ! ! !!!!!!!!!!!! !! 18° ! !!!!!!!!!!! !!!!!!! ! !!!!!! ! ! !!! Croydon !!!! ! Mount !! ! !!! ! ! Georgetown Surprise ! 0 100 200 300 400 ! !! !! !! ! ! !!! Kilometres !!!!! ! !!!!!!!!! !!! Greenvale ! ! !!!!! !! !!!! ! 20° !! !! ! !!! Richmond Hughenden Mount Coolon

! 22° !!!!!!! !!!!!!!!!!!!!!!!! !!!!!!!!!!!!!!! Winton Clermont !!!!!!!!!!! ! !!!!!!!!!!!!! !!!!!!!!!! Croydon Boulia !!! !!!!! !!! !!!!!!!

24° Anakie Bedourie Rolleston !!!!

26°

!! !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! Proston !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!!!!!!!!!!!!!!!!!!!!! !!!!

28° !!!! !! Pittsworth !!!!!

Dirranbandi Stanthorpe

30°

138° 140° 142° 144° 146° 148° 150° 152° 154° 08A/GD-01-08/figure7.cdr Figure 7. Figure 7: The location of diamond indicator minerals found in Queensland Queensland Geological Record 2008/04 21

9° CHROMITE CHROMITE GRAINS

! 1 - 1000 1001 - 3600 10° 3601 - 10500 Great Australian Basin Georgina Basin Carpentaria Basin Barnard Province Late Carboniferous - Triassic 10501 - 24000 Intracratonic Basins Cape River Province Late Devonian - Late Carboniferous Anakie Province Intracratonic Basins

NEOPROTEROZOIC - 24001 - 83700 Gympie Province EARLY PALAEOZOIC Iron Range Province Connors-Auburn Province Croydon Province 12° Texas Province Savannah Province Wandilla Province South Nicholson Basin Silverwood Province McArthur Basin Yarrol Province Etheridge Province Broken River Province Eastern Fold Belt Province

TASMAN OROGENIC ZONE 14° Coen Hodgkinson Province Western Fold Belt Province

PROTEROZOIC SHIELD Fork Lagoons Province Kalkadoon-Ewen Province Thalanga Province Murphy Province

Laura Geological boundary Cooktown Approximate geological boundaries of Carpentaria, 16° Palmer River Eromanga, Surat and Clarence-Moreton Basins !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! Subsurface geological boundaries of Late Carboniferous to Triassic Basins Subsurface geological boundaries of Early Devonian to Early Carboniferous Basins

! Atherton

18° Croydon Mount Georgetown Surprise 0 100 200 300 400

Greenvale Kilometres ! 20°

Richmond Hughenden Mount Coolon

22° Winton

!!! !!!!!!! Clermont Boulia ! Croydon

Anakie 24° Bedourie Rolleston

26° Proston !!!!! !!!!!!!!!!!!! !!!!!!!!!! !!!!!!!!!!

28° Pittsworth

Dirranbandi Stanthorpe

30°

138° 140° 142° 144° 146° 148° 150° 152° 154° 08A/GD-01-08/figure8.cdr Figure 8. Figure 8: The number of chromite grains found at each location 22 Cranfield & Diprose

9° PYROPE PYROPE GRAINS

! 1-44 45 - 136

10° ! 137 - 264 Great Australian Basin Georgina Basin Carpentaria Basin Barnard Province 264 - 500 Late Carboniferous - Triassic Intracratonic Basins Cape River Province Late Devonian - Late Carboniferous Anakie Province 501 - 920 Intracratonic Basins

TASMAN OROGENIC ZONE 14° Hodgkinson Province Western Fold Belt Province

Coen PROTEROZOIC SHIELD Fork Lagoons Province Kalkadoon-Ewen Province Thalanga Province Murphy Province

Laura Geological boundary Cooktown Approximate geological boundaries of Carpentaria, Palmer River Eromanga, Surat and Clarence-Moreton Basins 16° !!!!!!!!!!!!!!!!!! !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! ! Subsurface geological boundaries of Late Carboniferous to Triassic Basins Subsurface geological boundaries of Early Devonian to Early Carboniferous Basins Atherton

18° Croydon Mount Surprise Georgetown 0 100 200 300 400

Greenvale Kilometres

20°

Richmond Hughenden Mount Coolon

22° Winton

Clermont Boulia Croydon

24° Anakie Bedourie Rolleston

26°

Proston

28° Pittsworth

Dirranbandi Stanthorpe

30°

138° 140° 142° 144° 146° 148° 150° 152° 154° 08A/GD-01-08/figure9.cdr Figure 9. Figure 9: The number of pyrope grains found at each location Queensland Geological Record 2008/04 23

9° GARNET GARNET GRAINS

! 1-6 7-20

10° ! 21-80 Great Australian Basin Georgina Basin Carpentaria Basin Barnard Province 81 - 250 Late Carboniferous - Triassic Intracratonic Basins Cape River Province Late Devonian - Late Carboniferous Anakie Province 251 - 1500 Intracratonic Basins

TASMAN OROGENIC ZONE Coen 14° Hodgkinson Province Western Fold Belt Province ! !!! PROTEROZOIC SHIELD !!!! !!!!!!! !!!!!!! !!!!!!!! !!!!!! !!!!!! Fork Lagoons Province Kalkadoon-Ewen Province !!!!!!!!!!!! !!!!!! !!!!!!!! !! !!!!!!!!!!!!!! !! Thalanga Province Murphy Province

!!! 18° !! ! !!!!!! Mount Croydon Surprise Georgetown 0 100 200 300 400

Greenvale Kilometres

20°

Richmond Hughenden Mount Coolon

22° Winton

Clermont Boulia Croydon

24° Anakie Bedourie Rolleston

26°

! Proston

28° Pittsworth

Dirranbandi Stanthorpe

30° 138° 140° 142° 144° 146° 148° 150° 152° 154° 08A/GD-01-08/figure10.cdr Figure 10. Figure 10: The number of garnet grains (which have not been specifically identified as being pyrope) found at each location

Figure 10 shows the number of garnet grains (which have not been specifically identified as being pyrope) found at each location. Figure 11 shows the number of picroilmenite grains found at each location. Figure 12 shows the number of chrome diopside grains found at each location. 24 Cranfield & Diprose

9° PICRO ILMENITE PICRO ILMENITE GRAINS ! 1 - 190

10° 191 - 576 Great Australian Basin Georgina Basin Carpentaria Basin Barnard Province 577 - 2200 Late Carboniferous - Triassic Intracratonic Basins Cape River Province Late Devonian - Late Carboniferous Anakie Province 2201 - 4500 Intracratonic Basins

NEOPROTEROZOIC - Gympie Province EARLY PALAEOZOIC Iron Range Province Connors-Auburn Province Croydon Province 12° 4501 - 9500 Texas Province Savannah Province Wandilla Province South Nicholson Basin Silverwood Province McArthur Basin Yarrol Province Etheridge Province Broken River Province Eastern Fold Belt Province

TASMAN OROGENIC ZONE 14° Hodgkinson Province Western Fold Belt Province

Coen PROTEROZOIC SHIELD Fork Lagoons Province Kalkadoon-Ewen Province Thalanga Province Murphy Province

Laura Geological boundary Cooktown Approximate geological boundaries of Carpentaria, 16° Palmer River Eromanga, Surat and Clarence-Moreton Basins !!!!!!!!!!!!!!!!! Subsurface geological boundaries of Late Carboniferous to Triassic Basins Subsurface geological boundaries of Early Devonian to Early Carboniferous Basins

! Atherton

18° Croydon Mount Surprise Georgetown 0 100 200 300 400

Greenvale Kilometres !

20° !

Richmond Hughenden Mount Coolon

22° Winton

!!!! !!!!!!!!! Clermont Croydon Boulia !

24° Anakie Bedourie Rolleston

26° Proston ! !!!!!!!!!!!!!!!!!!!!! !!!!!!!!!!!! !!!!!!!!! !!!!!

28° !! Pittsworth

Dirranbandi Stanthorpe

30° 138° 140° 142° 144° 146° 148° 150° 152° 154° 08A/GD-01-08/figure11.cdr Figure 11. Figure 11: The number of picroilmenite grains found at each location Queensland Geological Record 2008/04 25

9° CHROME DIOPSIDE CHROME DIOPSIDE GRAINS

! 1-28 29 - 100 10° Great Australian Basin Georgina Basin 101 - 255 Carpentaria Basin Barnard Province Late Carboniferous - Triassic 256 - 480 Intracratonic Basins Cape River Province Late Devonian - Late Carboniferous Anakie Province Intracratonic Basins

NEOPROTEROZOIC - 481 - 1730 Gympie Province EARLY PALAEOZOIC Iron Range Province Connors-Auburn Province Croydon Province 12° Texas Province Savannah Province Wandilla Province South Nicholson Basin Silverwood Province McArthur Basin Yarrol Province Etheridge Province Broken River Province Eastern Fold Belt Province

TASMAN OROGENIC ZONE 14° Hodgkinson Province Western Fold Belt Province

Coen PROTEROZOIC SHIELD Fork Lagoons Province Kalkadoon-Ewen Province Thalanga Province Murphy Province

Laura Geological boundary ! Cooktown ! Approximate geological boundaries of Carpentaria, 16° Palmer River !! !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! Eromanga, Surat and Clarence-Moreton Basins Subsurface geological boundaries of Late Carboniferous to Triassic Basins Subsurface geological boundaries of Early Devonian to Early Carboniferous Basins

! Atherton

18° Croydon Mount Georgetown Surprise 0 100 200 300 400 Greenvale Kilometres !! 20°

Richmond Hughenden Mount Coolon

22° Winton

Clermont Croydon Boulia !!

24° Anakie Bedourie Rolleston

26°

!!! !!!!!!!!!!!!!!! Proston !!!!!!! !!!!!

28° !! !!!! Pittsworth

Dirranbandi Stanthorpe

30° 138° 140° 142° 144° 146° 148° 150° 152° 154° 08A/GD-01-08/figure12.cdr Figure 12.

Figure 12: The number of chrome diopside grains found at each location 26 Cranfield & Diprose

9° NIOBIUM QUANTITY NIOBIUM (ppm) ! 0.10 - 6.75 6.76 - 12.00 10° 12.01 - 23.00 Great Australian Basin Georgina Basin Carpentaria Basin Barnard Province Late Carboniferous - Triassic 23.01 - 47.00 Intracratonic Basins Cape River Province Late Devonian - Late Carboniferous Anakie Province Intracratonic Basins

NEOPROTEROZOIC - 47.01 - 150.00 Gympie Province EARLY PALAEOZOIC Iron Range Province Connors-Auburn Province Croydon Province 12° Texas Province Savannah Province Wandilla Province South Nicholson Basin Silverwood Province McArthur Basin Yarrol Province Etheridge Province Broken River Province Eastern Fold Belt Province

TASMAN OROGENIC ZONE 14° Hodgkinson Province Western Fold Belt Province

Coen PROTEROZOIC SHIELD !!! Fork Lagoons Province Kalkadoon-Ewen Province Thalanga Province Murphy Province

Laura Geological boundary Cooktown Approximate geological boundaries of Carpentaria, 16° Palmer River !!!!!!!!!!!!!!!!!!!! Eromanga, Surat and Clarence-Moreton Basins !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! ! Subsurface geological boundaries of Late Carboniferous to Triassic Basins Subsurface geological boundaries of Early Devonian to Early Carboniferous Basins Atherton 18° !!!!!!! Croydon !!!!!!! Mount Georgetown Surprise 0 100 200 300 400 Greenvale !!!! Kilometres

20°

Richmond Hughenden Mount Coolon

22° !!!!!!!! !!!!!!!! Winton

Boulia Croydon !!!!!! Clermont 24° Anakie Bedourie Rolleston

26°

!!!!!!!!!!!!!!Proston

28° Pittsworth

Dirranbandi Stanthorpe

30° 138° 140° 142° 144° 146° 148° 150° 152° 154° 08A/GD-01-08/figure13.cdr Figure 13.

Figure 13: Niobium (Nb) concentrations in ppm

Figure 13 shows niobium (Nb) concentrations in ppm. Note the high Nb values in the Mount Surprise area and in the southern part of the Mount Isa region. Figure 14 shows the location of grains that underwent microprobe analysis. Queensland Geological Record 2008/04 27

9° DMC

! DMC SAMPLE POINTS

TASMAN OROGENIC ZONE 14° Hodgkinson Province Western Fold Belt Province

Coen PROTEROZOIC SHIELD Fork Lagoons Province Kalkadoon-Ewen Province Thalanga Province Murphy Province

Laura Geological boundary Cooktown Approximate geological boundaries of Carpentaria, Palmer River Eromanga, Surat and Clarence-Moreton Basins 16° ! !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! Subsurface geological boundaries of Late Carboniferous to Triassic Basins Subsurface geological boundaries of Early Devonian to Early Carboniferous Basins !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!Atherton

18° Croydon Mount Georgetown Surprise 0 100 200 300 400

Greenvale Kilometres !!!!!!!!!!!!!!!!!!!!!!!!!! !!!!! !!!!!!!! !!!!!!!!!!!!!!! !!!!!!!!!!!!!!!!!!!!!!!!!!!!! ! !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! 20° !!!!!!!!!!!!!!!!!!!!!!!!!!! !!!!!!!!!!!!! !!!!!!!!!!!!!! Richmond Hughenden Mount Coolon

22° Winton

Clermont Boulia Croydon

24° Anakie Bedourie Rolleston

26°

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!Proston !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

28° Pittsworth !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! ! Dirranbandi !! !!!!!!!!!!!!!!!!!! !!!!!!!!!!!!Stanthorpe

30° 138° 140° 142° 144° 146° 148° 150° 152° 154° 08A/GD-01-08/figure14.cdr Figure 14. Figure 14: The location of grains that underwent microprobe analysis 28 Cranfield & Diprose

EXPLORATION FOR DIAMONDS IN QUEENSLAND 1960–2008

Diamond exploration in Queensland is outlined below by geographical region. Exploration has been carried out in the north-west, far north, central, south-west and south-east areas of the State. Overall, results have not been encouraging and currently only ~1% of exploration for diamonds in Australia occurs in Queensland (Jacques, 2006). Since 1960, more than 40 exploration companies have carried out some systematic exploration for diamonds in Queensland, including CRA Exploration Pty Ltd with more than 30 permits and Stockdale Exploration Ltd and Ashton Mining Ltd with more than 30 permits. For completeness, some of the exploration summaries below contain information on exploration for commodities other than diamond. Microdiamonds have been found in EPMs 3523, 3887, 3907 (held by Ashton Mining Ltd and containing the most occurrences), 3933, 3982, 4022, 9270 and 10713. Permits with diamond indicator minerals include EPMs 1692, 1693, 2349, 2470, 2471, 2489, 3046, 3886, 3907, 3931, 3933, 3973, 3982, 3987, 3988, 4026, 4064, 4206, 4207, 4707, 5000, 5117, 5336, 5629, 5688, 7245, 7284, 7846, 8683, 8690, 8997, 9687, 9720, 10084, 10192, 13506 and 13652. Analysis of indicator minerals was undertaken in EPMs 2490, 2057, 2058, 2059, 2060, 7224, 7284, 8997, 9720, 9768, 10048, 10049, 10192 and 11420. For details of the location of exploration permits in Queensland link to the interactive resource and tenure maps on the Departmental website at www.dme.qld.gov.au.

NORTH-WEST QUEENSLAND

EPMs 2349 and 2350 (Toomba Range), south-west of Mount Isa, were granted to Dampier Mining Company Limited in September 1980. These permits were taken out primarily to test the diamond potential of the area and also to test its potential for base metals. Interpretation of an aeromagnetic survey identified six anomalies that were potential kimberlite structures. The anomalies were located on the ground using ground magnetic surveys.

Twelve holes were drilled at the magnetic anomalies. Drill samples were analysed for Cu, Pb, Zn, Co, Ni and Nb. No kimberlitic materials or other significant geochemical anomalism were recognised. No further work was recommended.

EPM 2349 was surrendered in September 1981 and EPM 2350 was surrendered in December 1981.

EPM 3315 was granted to Queensland Mines Ltd and Urangesellschaft Australia Pty Ltd in September 1982. Exploration targeted the Lagoon Creek Fault in the Westmoreland area, which was known to be dyke-filled and contain uranium mineralisation. A magnetic survey was carried out over an established grid, but no obvious trends were discernible. Seven rock chip samples assayed 20ppm to 0.16% Cu, 10–30ppm Pb, 2–40ppm Zn, and <0.2ppm Au. Seven holes (1531m percussion and 609.6m core) were drilled to test the inferred extension of the dyke and intersected silica-rich zones in the Westmoreland Conglomerate and breccia zones in the Seigal Volcanics. No dyke material was intersected. Core Queensland Geological Record 2008/04 29 samples returned no significant uranium assay results. A radon survey to test for mineralisation along the fault zone returned negative results.

It was concluded that the brecciation and silicification encountered could indicate a fault zone, but that any dyke or associated mineralisation did not continue into the Permit area or is discontinuous and difficult to detect.

One stream sediment sample was collected and processed for kimberlitic indicator mineral analysis, but the results were not available at the time of the final report on the Permit. The Permit expired in June 1985.

EPM 3393 was granted to Queensland Mines Ltd and Urangesellschaft Australia Pty Ltd in March 1983. In 1983, exploration targeted structure-controlled uranium mineralisation along the Lagoon Creek Fault, particularly in an area where a previous Northern Territory drill hole had intersected significant uranium-gold mineralisation. Soil radon surveys were carried out over the inferred extensions of the Lagoon Creek Fault and Namalangi Fault; all results were low. Five percussion/core holes, including one redrill, were drilled for a total of 778.6m (255.6m percussion and 523.0m core). No dyke material was intersected. Split core samples (219 samples) generally assayed <0.1ppm Au; the highest assay result was 0.9ppm Au. The significant uranium–gold mineralisation reported from the previous hole could not be repeated even with drill holes only 5m distant. These results significantly downgraded the potential of the Lagoon Creek Fault Zone for Redtree style dyke-associated uranium-gold mineralisation. No samples for diamond indicator mineral analysis were collected from EPM 3393. No kimberlitic indicator minerals were found in samples collected from near the borders of the permit, which was relinquished in December 1985.

EPM 3474 was granted to Aquitaine Australia Minerals Pty Ltd and Elf Aquitaine Triako Mines Ltd in May 1983. The companies explored for base metals and diamonds in the Hedleys Creek area. Previous base metals exploration in the area was compiled and interpreted. Field exploration commenced with reconnaissance geological mapping of the Fickling Group at 1:25 000 scale, selected rock chip sampling, and detailed mapping at 1:5000 scale of seven areas covering ‘INPUT’ anomalies and known mineralisation. Geoterrex Pty Ltd carried out an EM survey follow-up of eight selected INPUT anomalies, reconnaissance ground magnetometer traverses and a high sensitivity aeromagnetic survey. The anomalies were attributed to lithological conductors rather than sulphide mineralisation. Mapping and drilling of two holes (234m rotary percussion and 310.6m core) indicated that carbonaceous shale/siltstone units of the Mount Les Siltstone, which contain high pyrite and minor zinc concentrations, offer the best potential for stratiform base metal mineralisation. Efforts to secure a joint venture partner for the area were unsuccessful and no further base metals exploration was carried out.

Stockdale Prospecting Ltd farmed into the Permit in 1984 to search for diamonds as part of an extensive exploration program in Queensland and the Northern Territory. Reconnaissance stream sediment sampling for diamonds and kimberlitic indicator minerals was carried out in 1985. Four stream sediment samples from Gorge, Wire and Hedleys Creeks were collected, examined for 30 Cranfield & Diprose heavy mineral content and analysed for kimberlitic indicator minerals. Two ilmenite grains and two spinels were found but considered to not be kimberlitic in origin but to have originated from Proterozoic age volcanics within the permit area. The Permit was relinquished in November 1985.

CRA Exploration Pty Ltd was granted EPM 3523 in June 1983. Exploration focused on investigations for uranium and diamonds near and downstream from Carpentarian age mineralisation associated with exposures of the Westmoreland Conglomerate.

A detailed airborne magnetic and radiometric survey was followed by ground magnetics and gravel sampling. Six of the 71 gravel sampling sites produced one microdiamond each; two microdiamonds were found in one sample. No kimberlitic minerals were found. Fourteen loam samples were collected over four anomalous areas identified by previous exploration. All of these samples returned negative results. Although several microdiamonds were located in this area, no source rock was identified and the Permit was relinquished in June 1984.

EPM 3671 ‘Westmoreland’ was granted to International Mining Corporation NL in May 1984. A stream sediment survey (170 samples) was carried out to delineate any diamond, gold, uranium or base metal occurrences in this Permit, which covered part of the Cliffdale and Scrutton Creeks areas. Exploration was supported by geological mapping, rock chip sampling and proton magnetometer and scintillometer traverses.

An air photo interpreted lineament analysis delineated numerous linear fault systems and circular structures that might be prospective for kimberlitic or lamproitic intrusions. Two circular structures were present in the northern part of the tenement. These structures were extremely magnetic. A heliborne stream sediment sampling program was carried out to test these structures. Geological inspection indicated that rocks in these areas contained clusters of pale clinopyroxene, intensely altered plagioclase and possible K-feldspar phenocrysts set in unaltered magnetite skeletal titaniferous oxides that are partly converted to leucoxene. Blue green amphibole, sphene, chlorite, epidote and pumpellyite and traces of carbonate and pyrite are the result of alteration. The southern structure was anomalous in gold, copper, zinc, chrome, bismuth, tin and magnesium. The northern structure, located 5km away, was anomalous in lead, nickel, chrome, titanium and magnesium. Heavy mineral concentrates from the stream sediment samples did not contain any kimberlitic indicator minerals, but sample quantities may have been too limited for these results to be conclusive. Despite this, the Permit was relinquished in August 1985.

EPM 3741 was granted to Urangesellschaft Australia Pty Ltd and Savage Exploration Pty Ltd in May 1983. Exploration targeted gold mineralisation within the Permit and SMLA 8030 (Buck Hill) in the Westmoreland area. Stream sediment, soil and rock chip sampling, as well as geological mapping and costeaning, were carried out. Results at Buck Hill provided evidence for gold shedding from a narrow east-trending quartz breccia zone that intersects the Buck Hill Fault. This zone was very low-grade and weakly developed and was not considered to warrant further investigation. Heavy mineral concentrates from Queensland Geological Record 2008/04 31 stream sediment samples were forwarded for analysis for diamond indicator minerals. No indicator minerals were found in any sample. The Permit was relinquished in May 1984.

EPM 3829 was granted to BHP Minerals Ltd in September 1984. The Permit, covering the Cliffdale Creek – Scrutton Creek area, was acquired to test an area of cover with intense dipolar negatively remnantly magnetised anomalies for possible carbonatite or kimberlite-hosted mineralisation. Ground magnetometer traverses were carried out over the aeromagnetic anomaly and four percussion holes (390m) were drilled to test its source. The first two holes intersected magnetic volcanic rocks. The third hole intersected 30m of sand above non-magnetic volcanic rocks. The fourth hole intersected non-magnetic volcanic rocks. The anomaly is apparently due to the magnetic remnance of the source rocks. Analysis of drill chip samples indicated no mineralisation. The Permit was relinquished in December 1984.

EPMs 3864 to 3878 were granted to Stockdale Prospecting Ltd in November 1984. These Permits covered ~3991km2 in the Hedleys Creek and Nicholson River areas. The company carried out regional prospecting for diamonds as part of a larger program involving tenements in the Northern Territory.

Limited ground reconnaissance was carried out in 1984. Twenty-seven reconnaissance stream samples were collected from significant drainages across all the Permits and processed for kimberlitic indicator mineral analysis. Samples returned negative results, with the exception of one para-kimberlitic ilmenite that was not considered significant. A geomorphological and Landsat study of the area was also carried out to assist with interpretation of exploration results.

An additional 25 samples were collected in 1985. Concentrates were sorted and examined but no diamonds were recovered. An analysis for kimberlite indicator minerals identified no, but a spinel was found in one sample from the Wire Creek catchment. This was considered to be sourced from the Cliffdale Volcanics.

The Permits were all relinquished in September 1985.

EPM 3887 was granted to CRA Exploration Pty Ltd in January 1985. This Permit, immediately west and south-west of the Mount Gordon (Gunpowder) mine was taken up to explore for diamonds in kimberlites.

Sixty-six gravel samples were collected and processed for kimberlitic indicator mineral analysis. Microdiamonds were recovered from two samples but no other kimberlitic minerals were located in this area. No diamonds were found in follow-up samples from the two sites, despite the processing of 12kg of sample. It was concluded that the two microdiamonds could be a result of contamination at the laboratory as no kimberlitic indicator minerals were found in the other samples. Alternatively, they could come from a secondary source in Proterozoic sediments or Mesozoic or Quaternary fluvial sediments. The absence of indicator minerals suggested that these diamonds were far removed from their primary source. Consequently, the area was not considered to be promising and no further work was recommended. The Permit was relinquished in November 1985. 32 Cranfield & Diprose

EPM 3907, in the Camooweal area, was granted to Ashton Mining Ltd in December 1984. Ashton Mining carried out exploration for kimberlite pipes as manager of the ‘Barkly Joint Venture’ with AOG Minerals Ltd, Aberfoyle Exploration Pty Ltd and Kennecott Explorations (Australia) Ltd. This extensive Permit covered the south-eastern part of the Lawn Hill 1:250 000 Sheet area, most of the Camooweal 1:250 000 sheet area and part of the Mount Isa 1:250 000 Sheet area.

Regional gravel sampling (407 samples) was carried out in 1985. Gravel samples were processed for kimberlitic indicator mineral analysis at Ashton Mining’s laboratory in Perth. Nineteen gravel samples were found to contain a total of 18 microdiamonds and one macrodiamond. One zircon, 12 chromite grains and several garnets were identified by laboratory examination but these were considered to be of non-kimberlitic origin.

Geoterrex Pty Ltd flew an aeromagnetic survey over 70% of the Permit. Geophysical interpretation led to the delineation of a number of targets. Follow-up investigations comprised ground magnetic surveys and soil (loam) sampling. Ninety-three microdiamonds and two almandine garnets were found in samples from the Mount Oxide area. Results from elsewhere in the Permit were negative for the presence of kimberlitic materials.

About 82% of the Permit was relinquished in March 1985. The two areas retained were within the Mount Oxide, Norfolk and Camooweal 1:100 000 Sheet areas, where most of the microdiamonds had been recovered.

Twenty-five gravel samples from the area straddling the Norfolk and Camooweal 1:100 000 Sheet areas were processed for kimberlitic indicator mineral analysis. Ten microdiamonds were recovered from seven samples as well as seventy-five garnets that were not considered to be of kimberlitic origin. Six hundred and thirty follow-up loam samples were collected. Four anomalous areas were selected for drilling. Drilling results were negative and the source of the magnetic anomalies was found to be a band of brown-red sand and silt. Despite the occurrence of microdiamonds, this area was considered unlikely to contain any kimberlite pipes and was relinquished in July 1985. The Mount Oxide area was retained because of the high incidence of microdiamonds recovered from gravel samples from this area.

Follow-up work in the Mount Oxide area in 1985 comprised gravel sampling (20 samples), rock sampling (15 samples) and ground magnetic surveys. Seven chromite grains were found but these were not considered to be of kimberlitic origin. and extensive loam sampling of two airborne magnetic anomalies. A photogeological study delineated 70 photo features that were field checked. One thousand five hundred and forty-eight loam samples were collected from nine anomalies and processed for kimberlitic indicator mineral analysis. Two hundred and forty-five microdiamonds and one macrodiamond were recovered from 217 samples, as well as three garnets and two chromite grains that were not considered to be of kimberlitic origin. Due to the high number of diamonds found in this area, it is considered to have potential for a kimberlitic source. Queensland Geological Record 2008/04 33

In 1986, Ashton Mining carried out a stratigraphic loam sampling program to determine the source of the microdiamonds. Thirteen sites were selected and 30 loam samples were collected from each site, for a total of 390 loam samples. Twenty-five microdiamonds and >1000 garnets were recovered from 23 samples. The garnets were not considered to be of kimberlitic origin. Results indicated a high incidence of microdiamonds in outcrop areas of the middle unit of the Whitworth Quartzite and other Palaeoproterozoic units. A 1000t bulk sample was collected from close to the headwaters of Fiery Creek and was processed through an on-site heavy mineral separation plant. The >3mm fraction was examined for diamonds in the field and the <3mm fraction was checked in Ashton Mining’s Perth laboratory. This bulk sample contained three gem quality diamonds of 1.0mm, 1.8mm and 2.7mm size (0.0045, 0.06 and 0.17 carats). It was concluded that this area has a definite source of diamonds and that further work was required to locate that source.

Three additional 1000t bulk samples were collected in 1987 to test the Seymour River and Sandy Creek drainage basins. Eight gem quality diamonds ranging in size from 1.0–2.2mm (0.0095–0.0815 carats) were recovered from the Seymour River sample. No diamonds were found in the Sandy Creek samples.

In the second half of 1987, the company carried out a program of regional bulk cyanide leach and -80 mesh stream sediment (232 samples) and rock chip (41 samples) sampling to determine the gold and copper-gold potential of the Permit area. Gold was targeted because it had been found in a number of the gravel samples collected during the diamond exploration. A small number of anomalous areas were identified for follow-up work. Follow-up gold exploration in 1988 comprised bulk cyanide leach stream sediment sampling and geological traversing. Results were disappointing.

Diamond exploration continued in 1988 with the collection of an additional bulk sample (two 20t samples) from the Fiery Creek catchment.

Follow-up bulk sampling of the Seymour River catchment comprised seven 100t gravel samples taken upstream of the initial site. Six samples returned a positive result, with the largest stone recovered being 0.1989 carats. Three costeans were excavated over two magnetic anomalies to establish a source rock for microdiamonds in the Fiery Creek Dome area. Bulk rock samples were crushed, processed and examined for diamonds. One microdiamond was recovered from weathered quartz-rich sandstone from one magnetic anomaly. Sandstone and quartzite of the Whitworth Quartzite at the other anomaly returned two microdiamonds and one >0.5mm pyrope garnet. No ultrabasic intrusives were intersected and the sampling results were insufficient to infer any direct conclusions as to the source of microdiamonds in the area. A review of the data by a recognised diamond consultant indicated that the discovery of a diamondiferous kimberlite pipe within the Permit was highly unlikely. The Permit was relinquished in December 1988.

EPMs 3931, 3933, 3934, 3936 and 3937 were granted to CRA Exploration Pty Ltd in February 1985. The company carried out exploration for diamonds in the Calton Hills area north of Mount Isa. 34 Cranfield & Diprose

Fifty gravel samples were collected from EPMs 3936 and 3931 and processed for diamond indicator mineral analysis. The results for all samples were negative. Seventy-five gravel samples were collected from EPM 3933. Single microdiamonds were recovered from three samples. One sample contained a grain of pyrope. Fifty-two gravel samples were collected from EPMs 3934 and 3937. No diamonds or kimberlitic indicator minerals were recovered.

Repeat and follow-up sampling of the areas where the three microdiamonds were recovered did not recover any additional diamonds. Six single grain occurrences of chromite and one occurrence each of pyrope garnet and picroilmenite were recorded. Microprobe analysis of the chromite grains showed them to not be of kimberlitic origin. It was concluded that the mineral occurrences are not part of a primary dispersion halo around an actively eroding source and the Permits were relinquished in December 1985.

EPM 4022 was granted to CRA Exploration Pty Ltd in June 1985. The company explored for kimberlite-hosted diamonds in the Buckley River area. Twenty stream sediment gravel samples were collected and analysed for kimberlitic indicator mineralogy. A single microdiamond was recovered, but repeat samples failed to produce similar results. No kimberlitic indicator minerals were recovered. The Permit was relinquished in December 1985.

Australian Ore and Minerals Ltd applied for EPMs 4928 to 4931 and transferred them to the Diamond Company NL in 1987 before they were granted in September 1987. The areas of the Permits, particularly EPM 4932, were reduced by the Department of Mines to conform to the boundaries of the newly proclaimed Lawn Hill National Park. The Permits lay between the ‘Coanjula kimberlite province’, 200km west-north-west of Lawn Hill, and EPM 3907, where Ashton Mining Ltd had discovered microdiamonds in gravel samples. It was postulated that structures controlling the location of kimberlitic intrusives in Proterozoic basement might pass through the Lawn Hill area. The limestones of the Georgina Basin were considered to be a secondary target for base metal deposits.

Diamond Company NL, a wholly-owned subsidiary of Carr Boyd Minerals, negotiated the right to use the Carr Boyd/Geoscan ‘advanced airborne multispectral scanner’ (AMSS) to prospect the tenements for exposed kimberlitic rocks and associated soils. This method records the electromagnetic radiation caused by the differential absorption, reflection and emission of sunlight falling on various kinds of rock and minerals. Kimberlite-related rocks and soils reflect and emit spectral bands that are distinctly characteristic. The AMSS survey was flown over the entire area of the tenements at a flying height calculated to produce 9m by 9m pixels. Data were processed and a number of enhanced images produced. No indications of ultrabasic rocks (including kimberlites and lamproites) or their derived soils were found, nor were there any identifiable alteration halos that could be attributed to base metal or gold deposits. The Permits were surrendered in August 1988.

Ashton Mining Ltd was granted EPMs 4993 to 5000 in October 1987, and EPMs 5125 and 5211 in January and February 1988. These Permits, along with EPM 3907, were the subject of the Barkly Joint Venture Agreement between Ashton Queensland Geological Record 2008/04 35

Mining Ltd, Aberfoyle Exploration Pty Ltd, Kennecott Explorations (Australia) Ltd and Australian Diamond Exploration NL. Ashton Mining managed the exploration, which targeted diamonds and gold.

Exploration included regional bulk sampling of 1540t of gravel from seven sites to test for the presence of diamonds. Follow-up bulk sampling of the Seymour and Thornton River catchments involved the collection and processing of 3850t of gravel and 300t of rock from forty sites.

Of the nine catchment areas sampled for diamonds, results from the Thornton and Seymour River drainages were the most encouraging, with eleven (0.3939 carats) and eight (0.2215 carats) diamonds being recovered from these drainages. The largest stone recovered from the Seymour River area measured 3.3mm by 2.8mm by 2.5mm (0.1989 carats) and was a clear, green, flat-faced octahedron. One macrodiamond measuring 2.2mm by 2.0mm by 1.5mm (0.0815 carats) was recovered from the Desert Creek catchment area. One sample was found to contain 16 chromites and almandine and andradite garnet grains. It was concluded that none of these grains were kimberlitic in origin.

A helicopter-supported gravel sampling program (13 samples) was carried out in EPM 4995 to locate any kimberlitic indicator minerals in the Thornton River and upper reaches of the Seymour River catchments. Three microdiamonds were recovered but no kimberlitic indicator minerals were identified.

An aeromagnetic survey was flown over most of the Mammoth Mines 1:100 000 Sheet area. Twenty potential target areas were selected for further investigation. The majority proved to be surficial and hard rock in nature. Ground magnetic and loam sampling surveys were carried out over three of the targets. One sample contained a microdiamond. One anomaly in EPM 4993 was open hole/core drilled to 127m depth. Cambrian cherts and siltstones overlying Proterozoic dolomitic siltstones were intersected. The magnetic response was interpreted as being due to lateritic gravels. A review of the data by a recognised diamond consultant indicated that the discovery of a diamondiferous kimberlitic pipe within the Permits was highly unlikely.

Gold and copper-gold mineralisation were targeted in 1988 with bulk cyanide leach and -80 mesh stream sediment and rock chip sampling, and geological traverses. Twenty-five stream sediment anomalies were followed up with additional BCL and -80 mesh stream sediment sampling and rock chip sampling. One of nine anomalies (>2.74ppb Au threshold) sustained by the follow-up work was further investigated. It was found to contain minor copper mineralisation associated with quartz veins in the Eastern Creek Volcanics. One rock chip sample assayed 0.35ppm Au. No further work was considered to be warranted in this area.

The Permits were relinquished in January and February 1989.

CRA Exploration Pty Ltd was granted EPM 5297 ‘Seymour’ in March 1988. The target was an untested bullseye aeromagnetic anomaly in the Seymour River area that had been identified from data collected by Ashton Mining Ltd under EPM 36 Cranfield & Diprose

3907. It was decided to test the anomaly with ground magnetics and drilling in case it might represent a kimberlite or significant base metal accumulation.

Exploration included stream sediment sampling, a ground magnetic survey, geophysical modelling studies, and reverse circulation and core drilling.

No mineralisation was noted in the drill hole, although traces of pyrite were associated with occasional carbonate veining in metadolerite. The source of the aeromagnetic anomaly was determined to be a magnetic metadolerite intrusion of no economic significance. The Permit was relinquished in August 1988.

CRA Exploration Pty Ltd was granted EPM 7245 in April 1990. The Permit covered a geomorphological feature (an undrained plateau) known as the ‘Desert’, west of Mount Oxide, and was taken out for diamond and base metals exploration. The company targeted two subtle dipolar magnetic anomalies (K1 and K2 — previously delineated by Ashton Mining Ltd) of possible kimberlitic affinity and theorised that the source(s) of diamonds could be in poorly drained areas covered with duricrust.

Exploration included ground magnetics, lag and loam sampling, stream sediment sampling, bulk sampling and RAB/percussion drilling.

Twenty-two loam samples were collected from overlying aeolian sands or streams draining the K1 and K2 anomalies and processed for analysis for kimberlitic indicator minerals. None of the 22 loam samples collected contained diamonds or kimberlitic indicator minerals. A chromite and picroilmenite were found in separate samples. Microprobe analysis indicated that the chromite was kimberlitic in origin. Repeat and infill loam samples were collected but none returned favourable results. Loam samples were also collected from several circular anomalies that were identified from air photos.

A RAB hole was drilled to test one of the anomalies but the hole was unable to reach the basement. Drill sample results were disappointing, returning maximum assays of 250ppm Pb, 130ppm Cu and 75ppm Zn. Drilling did not locate a source for the magnetic anomalies. A bulk sample was collected from the hole and processed for analysis for kimberlitic indicator minerals. Results were negative.

A hand-held magnetic susceptibility survey was carried out over the tenement and drill chips from current and previous drilling were tested. No potential magnetic source was identified. No further work was recommended and the Permit was relinquished in December 1992.

EPM 8209 ‘Esterina’ was granted to Mount Isa Mines Ltd in August 1991. The targets were diamonds and limestone suitable for flux purposes at MIM’s lead smelter in Mount Isa. The Permit covered the Undina area, east of Cloncurry, where MIM had a working limestone quarry. Ninety-two open-hole percussion holes totalling 290m were drilled. No additional limestone reserves, other than those known, were identified. Queensland Geological Record 2008/04 37

The MIM airborne magnetics database was examined in order to investigate the existence of magnetically and/or radiometrically anomalous zones. Several anomalous zones were identified and a joint venture was entered into with Stockdale Prospecting Ltd in August 1992 to allow Stockdale to search for diamondiferous kimberlites.

A ground magnetics survey over one anomaly was followed by surface mapping and collection of three heavy mineral loam samples. Assay results were negative. The samples were processed for kimberlitic indicator mineral analysis, with negative results. One RC hole was drilled to 130m. Samples were collected at regular intervals and magnetic susceptibility readings were measured down the hole. Twenty of the drill samples were processed for assessment for kimberlitic indicator minerals, but all were found to be negative. The Permit was relinquished in July 1993.

EPM 8913 was granted to Delta Gold NL in July 1992. EPM 10435 was granted to Delta Gold Exploration Pty Ltd in February 1995. The permits were taken up for gold, base metals and diamond exploration in the Mort River area, south of Cloncurry.

In 1993, soil samples were collected on a 500m grid over >80% of EPM 8913; highest assay results were 34.3ppb Au, 100ppm Cu, 60ppm Pb and 75ppm Zn. A 5km long by 500 to 200m wide, north-west-trending zone with >2ppb Au in BCL soil samples was delineated. Base metal anomalies were sourced from narrow gossans adjacent to quartz veins or within black shale. Rock chip samples assayed up to 2350ppm Cu, 1550ppm Pb and 430ppm Zn.

Infill BCL soil sampling was carried out to better define the large gold anomaly, which was refined into a number of smaller zones. Rock chip samples returned up to 0.12g/t Au (from a gossan adjacent to a metadolerite dyke). Regional and follow-up soil sampling were completed in 1993/94. Three multi-sample >5ppb Au anomalies were delineated. These anomalies were grid mapped and rock chip sampled for a best assay result of 3.27ppm Au.

In 1994/95, 52 open hole percussion holes (1040m) were drilled to test the gold anomalies. The better intersections included 20m at 0.24ppm Au, 10m at 0.36ppm Au, 6m at 0.44ppm Au and 2m at 0.99ppm Au. Follow-up RC drilling (2182m) on the SE grid returned 1m at 0.65ppm Au, 5m at 0.11ppm Au, 5m at 0.1ppm Au and 1m at 0.34ppm Au.

In 1995/96, exploration within EPMs 8913 and 19435 included soil sampling (951 samples), rock sampling (195 samples), geological mapping, 14 line kilometres of fixed-loop TEM surveys, and 148 air-track percussion drill holes (1534m). Better drilling intersections included 5m at 0.83g/t Au (including 1m at 1.95g/t Au) from a narrow ironstone band at a metadolerite-carbonaceous metasediment contact at Blue Flat.

In 1996/97, a 125Hz GEOTEM survey flown by Aberfoyle Resources in 1992 was assessed. BHP then flew a new survey at 25Hz and was better able to distinguish bedrock conductors from overburden effects. A target was delineated at Bustard 38 Cranfield & Diprose

Flat. Follow-up investigations included moving loop EM and gravity surveys. The EM anomaly was interpreted as being due to a surficial conductor associated with a magnetic and gravity low. This zone of deep weathering was postulated to be associated with a clay alteration zone (potentially with related Cu-Au or Au mineralisation) or a kimberlite. One percussion hole intersected a deeply weathered sequence of variably graphitic shale overlain by unusually thick Cretaceous shale that was weathered to clay. Follow-up core drilling in 1997/98 intersected polymictic, poorly consolidated breccia covered by a thick sequence of flat lying clays and carbonaceous and graphitic greywackes and shales. A number of multi-element geochemical and heavy mineral concentrate analyses were competed on core samples, with negative results for kimberlite or lamprophyre indicator minerals. Petrology indicated that some of the breccia fragments are formed entirely from or an rimmed by ‘non-shardic’ glass material, indicating ‘in situ melting processes’ at extremely high temperature and low pressure conditions such as meteorite impacts.

One percussion hole drilled at another anomaly returned 30m at 0.12% Zn (including 6m at 0.17% Zn) from silica-albite altered psammites and schists of the Kuridala Formation. A second percussion hole at a moving loop EM anomaly returned no significant geochemical results.

In the second half of 1998, one bulk drainage sample was collected and processed for analysis for kimberlitic indicator minerals, but no results were reported. A review of previous work was carried out. Nothing further was reported. The Permits were relinquished in February 2002 and July 2003.

EPMs 10092, 10093 and 10094 were granted to Mount Isa Mines Ltd in May 1994. These Permits were acquired to explore for possible diamond-bearing diatremes beneath the eastern margin of the Georgina Basin using airborne magnetics.

Sixteen anomalies, possibly representing pipe-like bodies, had been identified from an MIM regional aeromagnetic survey. Ground magnetic follow-up surveys indicated that seven of these anomalies exhibit dipolar characteristics similar to kimberlitic diatremes. Six heavy mineral loam samples were collected and processed for kimberlitic indicator mineral analysis. One sample, from EPM 10094, contained one chrome spinel. No other kimberlitic indicator minerals were found. Surface soil geochemistry samples were also collected but were not analysed.

Seven reverse circulation holes were drilled into the centres of individual anomalies and intersected highly magnetically susceptible quartz-clay sediments that were interpreted to represent lenses of sediment associated with a lacustrine deposit or sinkholes in the Tertiary Austral Downs Limestone. Composite drill samples were processed for analysis for kimberlitic indicator minerals, but none were found.

The Permits were relinquished in September 1995. Queensland Geological Record 2008/04 39

EPM 10187 was granted to Mount Isa Mines Ltd in July 1994. The target was diamondiferous diatremes interpreted from airborne magnetic and radiometric survey data flown in 1990. Four anomalies were identified as possible pipe-like bodies. These were relocated using ground magnetic surveys but only two (IGC 04 and IHD 15) were soil sampled. There were no kimberlitic indicator minerals in any of the samples.

One RC hole was drilled at each anomaly. No kimberlitic indicator minerals were found and the source of the anomalies was thought to be highly ferruginous intervals within quartz-clays. The potential for this area to produce a diamond-bearing source was considered to be low and the Permit was surrendered in September 1995.

Ashton Mining Ltd was granted EPMs 10713, 10714 and 10715 in September 1995. These Permits formed the Australian Diamond Exploration Joint Venture, with Ashton Mining as exploration manager. Reconnaissance stream sediment sampling and airborne EM were carried out. Between 1995 and 1997, 39 reconnaissance and follow-up gravel and loam samples were collected, returning five positive results for microdiamonds from EPM 10713. Nine EM targets were selected for field investigation and seven were drill tested with 279m of rotary air blast drilling. All drill samples returned negative results. The Permits were relinquished in December 1998.

CRA Exploration Pty Ltd was granted EPMs 10930 to 10933 in January 1996. EPM 10242 was granted to CRA Exploration Pty Ltd in September 1994 upon the conditional surrender and partial relinquishment of EPMs 6022, 8877 and 8981. These Permits covered the Cliffdale Creek – Scrutton Creek area, south of Westmoreland, and were considered prospective for uranium, gold and diamonds.

Exploration in 1996 comprised a review of previous exploration results, interpretation of airborne magnetic and radiometric data, collection of 53 -2mm gravel samples as part of a regional sampling program targeting diamonds in the Murphy Province, and two 2km long soil sampling and mapping traverses over the Wire Creek Sandstone. The results of the diamond exploration were not reported.

In 1997, the company acquired 1:25 000 aerial photography, digital elevation models and heliborne aeromagnetic and radiometric data. Geological mapping was carried out at 1:2500 scale. Twelve core holes were drilled to test uranium anomalies in the Cliffdale Volcanics and Westmoreland Conglomerate. Better intersections included 12m at 0.076% U and 0.26g/t Au, 3m at 248ppm U and 0.158g/t Au and 1m at 0.039% U. Lead isotope dating was carried out on microcrystalline galena in uraninite.

In 1998, heliborne radiometric and magnetic survey data were interpreted and radiometric anomalies delineated for ground follow-up. Rock chip sampling, petrological analysis and soil sampling were carried out. Rock chip samples returned up to 0.11% U. Soil sampling at the Tango prospect defined a coherent zone of elevated U and Mo geochemistry coincident with a heliborne uranium anomaly. 40 Cranfield & Diprose

EPMs 10931 and 10933 were relinquished in February 1999. EPM 10242 was relinquished in February 2000. EPMs 10930 and 10932 were relinquished in May 2000.

EPM 12551 was granted to Stockdale Prospecting Ltd and Dee Beers Australia Exploration Ltd in July 2003.

Four magnetic anomalies were identified in the Buckingham Downs-Chatsworth area, south-east of Djarra, from an AGSO aeromagnetic survey. More detailed airborne magnetic surveys were flown over these targets. Single, vertical, reverse circulation holes were drilled at each anomaly, and all intersected mafic rocks. Drill samples were processed for analysis for kimberlitic indicator minerals. No indicator minerals were found in any of the samples and it was concluded that no further work was required. The Permit was relinquished in November 2004.

EPMs 13652 and 14796 were granted to ACN 099 477 915 Pty Ltd, a wholly-owned subsidiary of Crossland Mines Pty Ltd (formerly Paradigm North Pty Ltd) in May 2002 and August 2005, respectively and formed the Tripod Project. The main targets were Mount Isa and Osborne style Cu-Au deposits in the Chatsworth area, 90km north-east of Boulia.

Initial exploration was carried out by Paradigm North Pty Ld and comprised a review of previous exploration results, data compilation, interpretation of geological and geophysical data sets and research on the geology of known mineralisation.

In 2003/04, Paradigm carried out a field reconnaissance, reconnaissance stream sediment sampling and analysis by low level scans for 63 elements, including precious metals and platinoids.

Eight reconnaissance heavy mineral samples were processed for diamond indicator mineral analysis. No indicator minerals were recovered. Chromite grains were found in two samples but these were identified as non-kimberlitic. Metamorphic minerals such as kyanite and staurolite were also recovered. The company decided to discontinue diamond exploration in this area.

In 2005/06, Crossland Mines Pty Ltd carried out ground magnetic surveys over the most obvious geophysical features derived from the airborne surveys. Reconnaissance and rock chip samples were collected to explain the presence of metamorphic minerals that might indicate windows of prospective Proterozoic basement rocks. It was found that they could be derived from coarse pebble/cobble bands with clasts of Proterozoic metamorphic rocks in Cretaceous sediments.

No further work was considered necessary and the Permits were relinquished in January 2007. Queensland Geological Record 2008/04 41

COEN AREA

EPM 2810 was granted to Sturts Meadows Prospecting Syndicate NL in January 1981. A preliminary report mainly assessed gold and silver deposits, but also indicated that geological features of the area are compatible with possible kimberlitic structures. The report suggested that a reconnaissance program of bulk stream sediment sampling should be carried out to see if there is any possibility of kimberlitic structures in this area.

Mines associated with the Coen Shear Zone in the Coen area were examined under EPM 2810 and ML 651 (over the Great Northern mine). Many of the old workings were located, mapped in detail and sampled (although the names assigned to some of the workings are not correct). It was postulated that there was potential for low-grade gold mineralisation in cross fractures west of the shear zone.

Five prospects, including the Great Northern, were tested by shallow, angled percussion drilling. Later, it was realised that the drill rig used probably did not return accurate samples. Consequently, three core holes were drilled at the Great Northern mine. Two nearby Cook Shire Council water bores were also logged. Two of the core holes returned low-grade gold, with a few, localised higher assay results. The third hole returned lower grades than in an adjacent Consolidated Mining Industries Ltd hole. Subsurface results were poorer than surface sampling and it was suggested that there had been some surface enrichment in gold. Mapping and sampling of other old mines returned some sporadic high gold grades, but the mineralised quartz veins were generally narrow. It was postulated that economic, mineralised quartz veins are located at inflection points along the Coen Shear Zone, but these are difficult to locate and define. Recommended additional percussion drilling on prospects along the Coen Shear Zone was not carried out.

The company found that gold mineralisation in the northern part of the main Klondyke workings occurs in narrow (<2m wide) lenticular quartz pods parallel to major, milky white quartz reefs that have been hydrothermally injected into north-trending shear zones. Because assay results were low, follow-up work was cancelled. Similar reefs occur to the east in the old Breakfast Creek mining area, near the headwaters of the northern branch of Breakfast Creek and on the eastern fall of the range.

No sampling for potential kimberlites was carried out before the Permit was relinquished in December 1983.

S and B Ribich and L Leoni were granted EPM 3978 in March 1985. The Permit covered the Rocky River, north-east of Coen. The tenure holders entered into a joint venture with Alberta Mines NL. Alberta Mines also entered into an option agreement with B Tasic for rights over ML 2918.

In 1985, Alberta Mines reported that an outcrop of olivine nephelenite in this area showed promise for kimberlites and diamonds. One bulk sample was collected and sent for processing for kimberlitic indicator mineral analysis, but no results were reported. 42 Cranfield & Diprose

A prospectus dated October 1985 reported that sampling of gravels in the present stream bed in Zone B returned high gold grades averaging 18.83–21.54g/m3 along a 2.2km length. However, subsequent press releases by the company following bulk sampling of both the gravels in the stream bed and the adjacent alluvial terraces in 1986 reported disappointing results, with maximum gold grades of only 0.23g/m3 in the stream bed, and much lower grades in the alluvial flats (in Zones A and B). The earlier sampling was apparently based on unrepresentative small samples influenced by boulders in the stream bed. In any case, the results were never applicable to the alluvial flats. No further work was carried out by the company and the Permit was relinquished in March 1988.

EPM 3987 was granted to Mount Isa Mines Ltd in May 1985. Carpentaria Exploration Company Pty Ltd explored for possible diamonds and gold associated with an olivine nephelinite plug in the Stewart River area, 48km south-east of Coen. Stream sediment samples were assayed for gold and 16 other elements but results were disappointing. Bulk samples were collected and processed for kimberlitic indicator mineral analysis. The results indicated no signs of kimberlitic indicator minerals in any sample. The Permit was relinquished in February 1986.

EPM 3988 was granted to Mount Isa Mines Ltd in May 1985. The targets were diamond indicator minerals and/or gold and other elements in the Holroyd River area, 50km south-west of Coen. Bulk stream sediment sampling was carried out but negative results were obtained for gold and base metals. The Permit was surrendered in February 1986.

EPM 3989 was granted to Mount Isa Mines Ltd in May 1985. The targets were diamond indicator minerals and/or gold and other elements in the Lukin River area in the Kalkah 1:100 000 Sheet area, south of Coen. A bulk stream sediment sampling survey was carried out; a sample from Fish Creek assayed 400ppm Sn, reproducing a Sn anomaly identified by CRA Exploration Pty Ltd in EPMs 1736 and 1737. Samples were processed for analysis of kimberlitic indicator minerals. Many garnets were found in the samples but none were of kimberlitic origin. No other kimberlitic indicator minerals were found. The Permit was relinquished in February 1986.

EPM 5114 ‘Massey River’ was granted to Talisman Mining and Exploration Pty Ltd in January 1988. Astrik Resources NL, in a joint venture with Talisman, carried out exploration for heavy minerals in adjoining permit areas, but no work was done in EPM 5114. The Permit was relinquished in October 1988.

EPMs 5115, 5116 and 5117 were granted to Astrik Resources NL in January 1988 and EPM 5118 was granted in July 1988. The company explored for rutile, zircon, ilmenite, diamonds and monazite in the Stewart River, Balclutha Creek and Annie River areas, south-east of Coen.

Previous exploration by Pat Barron since the 1940s and later by P Barron and A O’Toole in the Cape York area defined anomalous heavy mineral concentrates in many of the river systems. In addition to gold and tin, significant concentrations of ilmenite, zircon and monazite were located. Xenotime was found in EPM 5117, where additional sampling confirmed the Annie River as being moderately Queensland Geological Record 2008/04 43 prospective for heavy minerals. Heliborne scintillometer traverses and ground inspections were carried out in this area.

Exploration involved surface and auger sampling of gravels from creek banks. In situ heavy mineral concentrates were visually inspected with a binocular microscope for diamond indicator minerals but no results were reported. Heavy mineral concentrates assayed up to 1750ppm Ce, 460ppm Y, 440ppm Nb, 690ppm Zr and 1.51% Ti. Astrik Resources was particularly interested in the monazite and xenotime content of the sands, but no further work was done.

EPMs 5117 and 5118 were relinquished in June 1989. EPM 5116 was relinquished in January 1990. The renewal of EPM 5115 was rejected in August 1992 as a result of failure to submit a report outlining the results of exploration.

Peko Exploration Ltd, a division of Peko-Wallsend Operations Ltd, was granted EPM 7656 ‘Merluna’, 130km north-west of Coen, in January 1991. The area was selected to cover two, discrete, negative aeromagnetic anomalies without attendant magnetic positive features. A 300 line kilometre aeromagnetic and radiometric survey was flown to obtain better data for estimating the depths to the targets by magnetic modelling.

Magnetic modelling indicated that the vertical depths to the targets were 170m and 290m. Aeromagnetic interpretation indicated that the most likely geological cause for the anomalies was dolerite plugs, rather than a kimberlitic source. The Permit was relinquished in June 1993.

EPMs 8682 ‘Scrubby Creek’, 8683 ‘Kirby’s Creek’, 8684 ‘Albert Spring’ and 8690 ‘Balclutha Creek’ were granted to CRA Exploration Pty Ltd in February 1992. The company explored for Au and diamonds in an area centred on Scrubby Creek, 11km west-south-west of Lily Vale Homestead.

The permits were applied for to cover airborne magnetic anomalies identified from recently released Bureau of Mineral Resources data. These targets were considered prospective as hosts for gold-base metals porphyry-related mineralisation, or to possibly represent diamondiferous diatremes.

In 1992, exploration comprised the collection and analysis of 232 bulk cyanide leach and 232 -80 mesh stream sediment samples, 148.9 line kilometres of helimag traversing of 15 aeromagnetic anomalies, and collection of thirteen -2mm gravel and two -2mm loam samples. Nine of the gravel samples were found to contain chromite grains in abundant quantities. These chromite grains were then forwarded for SEM analysis, but were found by Minplex Resources Pty Ltd to be inconsistent with kimberlite-derived chromites.

No field work was carried out in 1993 and 1994. A review of the exploration data indicated a low potential for economic mineralisation. EPMs 8683, 8684 and 8690 were relinquished in September 1994. EPM 8682 was relinquished in December 1993. 44 Cranfield & Diprose

EPM 8926 ‘Terrible Creek’ was granted to CRA Exploration Pty Ltd in August 1992. Exploration was for gold and diamonds in an area centred on the Stewart River, 50km south-east of Coen.

The permit was applied for to cover an airborne magnetic anomaly identified from the 1991 BMR Ebagoola aeromagnetic survey. This anomaly was considered prospective as a possible porphyry-related gold or base metal target or alternatively, as a mantle-derived diatreme prospective for diamonds.

The Proterozoic Newbery Metamorphics are overlain and obscured by an extensive veneer of Cainozoic residual sands. They comprise amphibolite-grade metamorphic rocks, including biotite-muscovite-quartz schist, quartzite, biotite-quartz-feldspar gneiss and amphibolite. Cainozoic cover includes the late Miocene Lilyvale beds (a clayey quartzose sand unit with variable gravel) in part overlain by a Quaternary alluvial component.

A discrete airborne magnetic target (EB6) adjacent to the permit was tested with a single helimag traverse. A gravel sample from a stream draining the anomaly did not contain any diamond indicator minerals or microdiamonds. A bulk cyanide leach stream sediment sample collected in conjunction with the gravel sample returned 1.5ppb Ag, 0.2ppm Au and 0.67ppm Cu. A -80 mesh stream sediment sample assayed 0.1ppm Ag, 0.9ppm As, 0.7ppm Bi, 0.1ppm Cd, 2.0ppm Cu, 0.4ppm Mo, 6.0ppm Pb, 0.6ppm Sb and 11.0ppm Zn.

No further work was considered warranted and the Permit was surrendered in August 1993.

LAURA AREA

Stockdale Exploration Ltd was granted EPM 523 in September 1968. As a result of initial low-density heavy mineral sampling in 1967 and 1968, the company concluded that ultrabasic rocks such as kimberlites might occur in the Laura area.

In September 1968, Stockdale Exploration collected seven bulk gravel samples, 67 small stream samples and 67 gully/loam samples. Minerals found in bulk gravel samples included zircon, olivine, garnet, ilmenite, chrome diopside, corundum/sapphire, topaz and ironstone. None of the concentrates indicated economically viable mineralisation. The stream and gully/loam samples were collected in order to locate any ultrabasic bodies in the area and also to see if further bulk sampling was required. These samples did not return any unusual results but did help to delineate some anomalous areas. It was considered unlikely that there were any ultrabasic source rocks in this area. The most likely source of the heavy mineral grains was re-worked terrace or flood plain deposits of an older Laura River. It was considered unlikely that the area concerned contained any diamonds of economic significance.

Stockdale Exploration continued the exploration program during the October–December 1968 period. Thirteen bulk gravel samples, 88 smaller gravel samples, 184 loam samples and 32 geochemical samples were collected. Heavy Queensland Geological Record 2008/04 45 minerals found included garnet, ilmenite, olivine, zircon, epidote and zoisite, ironstone, pyroxene, corundum, volcanic glass and cassiterite, but not in economic concentrations. Additional sampling was carried out to determine heavy mineral dispersion patterns in the search for any ultrabasic bodies. Follow-up sampling of sites that had returned promising first-pass results did not improve their prospectivity.

In one area, a well defined depression at the head of a creek was identified in air photos. The depression had no bedrock exposure and the results of samples from this area did not provide any conclusive evidence regarding mineral potential. There were indications of an ultrabasic body in one area, but the rock type could not be established. Overall, exploration results indicated that no economically viable minerals were present in this area and further sampling would not be beneficial. The Permit was relinquished in April 1969.

PALMER RIVER AREA

Tennyson Minerals NL was granted EPMs 2470 and 2471 in June 1980. The targets were gold, sapphires and diamonds in the Palmer and South Palmer Rivers and their tributaries. Extensive zones of gold-bearing alluvium were located along the Palmer River and Doughboy, Spear and Blackfellow Creeks. Sapphire and ruby were found in the alluvial deposits of Spear Creek. Percussion drilling of a prospective hard rock gold area in the Hodgkinson Formation did not locate any significant zones of gold mineralisation. Bulk sampling and testing of alluvium led to the delineation of alluvial gold resources in several streams. Several mining leases and claims were pegged.

An air photo interpretation identified several topographic depressions interpreted as weathered ultrabasic plugs. Stream sediment sampling was carried out over these areas and samples were analysed for niobium. Follow-up samples from areas with anomalous niobium were analysed for Nb, Ni, Co and Cr. Some anomalous niobium areas returned results indicative of ultrabasic rocks. High magnesium pyrope and picroilmenite were found in some heavy mineral samples, providing additional evidence for possible kimberlitic rocks or ultrabasic plugs.

Two costeans were sampled in one depression that had been infilled with sediments. These costeans exposed greenish clay with horizontal bands of magnesite. No source for the magnesite was found in surrounding rocks and it was concluded that the magnesite had been brought up from a magnesium-rich source by groundwaters. This indicated a high probability for ultrabasic rocks or a kimberlite pipe beneath the cover sediments in the depression.

The Permits were relinquished in June 1983.

EPM 2489 was granted to Oilmin NL, Transoil NL and Petromin NL in July 1980. The companies carried out reconnaissance sampling along the headwaters of the North Palmer River, west of Mount Lukin. River gravels were tested by bulldozer costeaning (31 costeans) along a 5km stretch of the river. Gravels at or near bedrock were sampled and panned. It was concluded that there was insufficient gold in the 46 Cranfield & Diprose gravels to warrant further testing. Stream sediment samples from the headwaters of the North Palmer River were assayed for Ta and Nb. Three low-order Nb anomalies were defined in creeks draining basalt flows. The samples were then analysed for Cu, Pb and Zn. Follow-up samples were analysed for Ta, Nb, Cu, Pb, Zn, Co, Ni and Cr in order to better define these anomalies. Samples were also collected for examination for diamond indicator minerals; only two pyrope garnets were found. The companies concluded that there were no ultrabasic rocks in the area. The Permit was relinquished in December 1981.

EPM 3174 was granted to Tennyson Minerals NL in December 1981. The targets were alluvial gold and possible gemstones to the west of the coastal divide in the headwaters of the Palmer River and its tributaries, including Spear Creek. Regional and check mapping did not result in finding any intrusive igneous bodies, despite some features that were identified in an initial air photo interpretation. There may be buried igneous sources, but a drilling program would be required to locate them. No further work was carried out because the diamond potential was consider as low in this area. A mining lease was applied for over an alluvial gold prospect. The Permit was relinquished in November 1982.

EPM 9019 ‘Strathleven 1’ was granted to CRA Exploration Pty Ltd in September 1992. The permit was taken up to evaluate airborne magnetic anomalies identified from the AGSO Hann River aeromagnetic survey. These anomalies, south of the Palmer River near Strathleven, 120km south-west of Laura, were interpreted as possible base and/or precious metal mineralised porphyry systems or as mantle-derived ultramafic diatremes with diamond potential.

No work was carried out on the permit before it was relinquished in December 1993.

EPM 9020 ‘Emu Creek 1’ was granted to CRA Exploration Pty Ltd in September 1992. This permit, in the Kennedy River area west of Laura, was taken up to evaluate airborne magnetic anomalies identified from the AGSO Hann River aeromagnetic survey. Interpretation of the airborne magnetic data suggested that the basement rock types were magnetic and non-magnetic deformed Proterozoic metamorphic rocks intruded by magnetically quiescent Silurian–Devonian Aralba Adamellite. These were considered to potentially represent a porphyry system, with possible associated base and/or precious metal mineralisation. Alternatively, they might represent mantle-derived diatremes, with potential for diamonds.

Most of the permit area is overlain by the Cainozoic Bulimba Formation, which forms part of the Karumba Basin. This unit consists of poorly exposed fluvial sandstone, claystone and conglomerate. In the east, a small area of Carpentaria Basin sediments (Rolling Downs Group), consisting of partly calcareous siltstone, mudstone and sandstone, is obscured by a thin veneer of Tertiary to Quaternary silts and sands. A review of the magnetic data indicated a depth to basement of 100–150m, downgrading the potential for discovery of near-surface porphyry-related mineralisation.

No field work was carried out, due to work commitments elsewhere, before the Permit was relinquished in December 1993. Queensland Geological Record 2008/04 47

COOKTOWN AREA

EPM 3046 was granted to Oilmin NL, Petromin NL and Transoil NL in May 1981. The Permit covered the old West Normanby Goldfield at Butchers Hill, south-west of Cooktown.

Five hundred and one -10 mesh stream sediment samples were analysed for Nb. The -72 mesh fraction of any sample that returned >20ppm Nb was then analysed for Nb, Cr and Ni to assess whether there were any ultrabasic sources in the area. Results indicated that the Mount Scatterbrain area might contain an ultrabasic source, possibly ultrabasic xenoliths in basalt. Two bulk samples were collected in this area to identify any diamond indicator minerals. No diamonds were found and only minor pyrope and olivine were recovered. It was concluded that, without finding any actual diamonds, further work on this area would be too costly and time consuming.

Stream gravels were panned for gold. The best results came from the Twins and Isabella–Monte Cristo areas. Follow-up costeaning was carried out, with inconclusive results. It was concluded that there was low potential for large tonnage, low-grade gold deposits at West Normanby. The Permit was relinquished in August 1982.

Oilmin NL, Transoil NL and Petromin NL were granted EPM 3238 in May 1982. These companies explored for diamonds in kimberlites and alluvial deposits in the McLean Volcanic Province, 50km west-south-west of Cooktown.

Air photo interpretation was used to identify any possible kimberlitic intrusions, but none were found. No diamonds had been previously found in this area and no gravel samples were collected. Existing aeromagnetic and radiometric data were analysed to delineate any anomalies, but none were found. The Permit was relinquished in July 1982.

EPM 5164 ‘Kings Plains’ was granted to Astrik Resources NL in January 1988. The company explored for Sn, Au and rare earths in an area centred on Kings Plains Lake, 12km west of Helenvale.

Astrik Resources entered a joint venture agreement to carry out a helicopter-assisted program of stream sampling, followed by RC drilling in some of the major stream systems in the Kings Plains area. Concentrates were submitted for mineragraphic examination. Laboratory testing on the heavy sand fraction showed broad regional patterns of heavy mineral deposits. The samples were also tested with a scintillometer and some readings were considered anomalous.

Eleven reverse circulation and power auger holes were drilled within or close to the Kings Plains swamp. RC holes 213 to 273 were drilled in the Kings Plains Lake area and intersected clay and gravel but failed to reach the projected heavy mineral gravel layers. The samples were not assayed. However, previous exploration had indicated a potential resource of 168 million yards at 3.2oz/cubic yard cassiterite over a thickness of 40m. 48 Cranfield & Diprose

No kimberlitic indicator minerals were located and the Permit was relinquished in November 1988.

EPM 5167 was granted to Astrik Resources NL in January 1988. The target was heavy minerals, particularly ilmenite, in an area centred on the Annan River, 20km south-west of Cooktown. Astrik Resources initiated joint venture with two prospectors to explore the area.

A reconnaissance helicopter-assisted program of stream sampling was followed up RC drilling in some of the major stream systems. Sixty-two sand samples were collected and 15 RC holes were drilled in or adjacent to the Annan River. The majority of the holes failed to intersect gravel beds and drill cuttings yielded low heavy mineral concentrations. Samples returned very low Y contents.

No kimberlitic indicator minerals were located and the Permit was relinquished in November 1988.

EPM 7284 was granted to Australian Consolidated Minerals Ltd in August 1990. The company explored for diamonds in an area centred on the western tributary of Wallace Creek, 13km south of Lakeland Downs and south-west of Cooktown.

Three prominent ovoid depressions (Bull Hollow, Tom’s Hollow 1 and Tom’s Hollow 2) were interpreted as possible kimberlitic pipes. Bull Hollow is in the headwaters of the Laura River, whereas Tom’s Hollow is in the headwaters of the Palmer River. Diamonds have been recovered from both the Palmer and Laura Rivers as a result of alluvial gold mining operations. Queensland Metals reported that their open hole drilling and costeaning data indicated that the Bull Hollow feature was underlain by weathered clay units. It was hoped by Australian Consolidated Minerals Ltd that the clay would turn out to be weathered kimberlite.

Three clay samples, a panned concentrate, and two rocks were collected from the Bull Hollow area and analysed for kimberlitic indicator minerals. Magnetite, ilmenite, brown spinel, garnet, orthopyroxene, clinopyroxene, zircon, brookite and chrome diopside were found in panned concentrate samples and were forwarded for SEM analysis and 15 grains underwent microprobe analysis. It was found that the spinels and pyrope garnets were kimberlitic and the picroilmenite and chrome diopside were probably kimberlitic. Some pink zircons were also considered to be possibly kimberlitic in origin. Two bulk samples were collected from Bull Hollow and Tom’s Hollow. No macrodiamonds were recovered.

Two holes were drilled at Bull Hollow. Hole BH 001 was drilled by air core to 123.0m and then by diamond drilling to 127.6m. It was sited near the centre of the Bull Hollow feature. Hole BH 002 was some 260m south of BH 001, approximately half way between BH 001 and the margin of the Bull Hollow feature. It was drilled to 100m using RC air core.

Heavy mineral samples were collected at regular intervals in both drill holes. All samples recorded numerous chromites, chrome diopsides and pyropic garnet. Thirty-three grains were sent for microprobe analysis and were found to be Queensland Geological Record 2008/04 49 possibly kimberlitic in origin. Whole rock geochemistry was carried out on the drill hole samples but provided little information.

An additional five bulk samples were collected and processed for macrodiamonds and none were recovered. The Bull Hollow feature was interpreted as an explosion breccia pipe that was later infilled with marginal coarse clastic sediments, followed by quiescent lacustrine clays and muds. Indicator minerals found at Tom’ Hollow were similar to those from Bull Hollow. The Permit was relinquished in December 1991.

EPM 7846 ‘Tom’s Camp’ was granted to JW Withers in June 1991. Diamond exploration was centred on the northern tributary of the Little Palmer River, 16km south-west of Lakeland Downs, and was carried out by Australian Consolidated Minerals.

Tom’s Camp is a prominent ovoid depression that was interpreted as a possible kimberlitic pipe. It is in the headwaters of the Palmer River where some diamonds have been recovered a result of alluvial gold mining operations. Three prominent ovoid depressions (Bull Hollow, Tom’s Hollow 1 and Tom’s Hollow 2) were delineated using aerial photography.

Two heavy mineral samples were collected — TH-1 from a stream emanating from Tom’s Hollow and WH-1 from a stream emanating from a small satellite pipe-like feature south-east of Toms Hollow. Both samples contained numerous diamond indicator minerals, similar to those found at Bull Hollow. Microprobe analyses showed that the spinels (high MgO, low Cr and high Al2O3) and garnets (Dawson: classification 9) are kimberlitic and that the chrome diopside is probably kimberlitic.

Investigations carried out at Tom’s Camp, indicated the ovoid depression to be a mantle-derived vent that was later infilled with marginal coarse clastic sediments, followed by quiescent lacustrine clays and muds.

Five concentrate samples were collected from downstream of Tom’s Hollow. Although many indicator minerals were recovered, no macrodiamonds were found. No further work was recommended and the Permit was relinquished in June 1992.

EPMs 9687, 9720, 9721, 9766 and 9768 were granted to Savage Resources Ltd in December 1993. They formed the Lakeland–Byerstown diamond exploration project, centred on Lakeland Downs.

The alkaline McLean Basalt of the Lakeland Downs area carries a variety of mantle-derived xenocrysts and some corundum. The Byerstown Range hosts two large diatreme vents that are located at obvious structural foci. Last century, diamonds were reported in the gold-bearing alluvium of adjacent major river systems. Recently, a reputed diamond was found in alluvium close to a McLean Basalt crater (Hoskins Crater) ~5km north-west of Lakeland Downs. 50 Cranfield & Diprose

The area is noteworthy for well developed diatreme vents that manifest deep-seated explosive volcanism, possibly originating from mantle depths. Such eruptions could conceivably have transported diamonds to the surface. The association of diamond with alkali basalt and corundum in other parts of eastern Australia encouraged Savage Resources Ltd to undertake preliminary diamond exploration in the Lakeland–Byerstown area.

Savage Resources reviewed previous diamond exploration reports and carried out further work in and about the Bull Hollow, Toms Hollow and Toms Hollow South diatremes on the Byerstown Range. An attempt was made to confirm the recent reputed macrodiamond find near Lakeland Downs.

Field and laboratory work included the collection of stream sediment, loam and rock samples for the recovery of indicator minerals and diamonds, reinterpretation of drill hole data from Bull Hollow, chemical analyses of indicator mineral grains, and ground magnetic traverses at the Bull Hollow, Toms Hollow and Toms Hollow South diatreme craters.

Eight samples were collected for determination of kimberlitic/lamproitic indicator mineralogy and microdiamond analysis. Two microdiamonds of uncertain origin (contamination suspected) were obtained from a stream sediment barrage sample collected at Toms Hollow but no macrodiamonds were recovered.

The morphology of some indicator minerals indicated a likely kimberlitic affinity. However, the indicator minerals from Bull Hollow and Toms Hollow, and their chemistry, are similar to those for the alkali basalts with which macrodiamonds are associated elsewhere in eastern Australia. No indicators of undoubted kimberlitic/lamproitic affinity were found.

Eight samples were collected and processed for kimberlitic indicator mineral analysis. Various indicator minerals were found in the samples, such as pyrope, chrome diopside, chromite, picroilmenite and two microdiamonds of uncertain origin (contamination suspected). Air photo interpretation was also carried out over the area and was used to identify features that might represent kimberlitic structures. Ground magnetic surveys were carried out over three of the main features. Indicator mineral grains were selected for further microprobe analysis. Many of the grains showed a chemistry that, although compatible with a kimberlitic mineral source, was not conclusively kimberlitic. The indicator minerals from Bull Hollow and Toms Hollow, and their chemistry, are similar to those for the alkali basalts with which macrodiamonds are associated elsewhere in eastern Australia.

It was concluded from the prospecting results and reviews that the Byerstown–Lakeland area is not prospective for significant diamond mineralisation. The Permits were relinquished in March and April 1995. Queensland Geological Record 2008/04 51

ATHERTON TABLELAND

EPM 3982 was granted to CRA Exploration Pty Ltd in March 1985. The company targeted diamond-bearing intrusive rocks and gold mineralisation associated with quartz breccias and veins in an area centred on the Walsh River, 30km south-west of Mareeba. This area was selected as a possible source for diamonds found in the O’Brien’s Creek gemfields near Mount Surprise. The tenement area covered a sequence of Hodgkinson Formation sediments and a variety of presumably younger volcanic and intrusive rocks, predominantly associated with the Parada Dyke Swarm to the west. Granite intrudes the sediments in the central tenement area and much of the northern area is covered by shallow alluvium. Antimony mineralisation is associated with quartz veins, predominantly in granite. Gold mineralisation is associated with arsenic and base metals in sulphide-cemented breccias and quartz vein sets within Hodgkinson Formation sediments.

One hundred and sixty-seven gravel samples were collected during reconnaissance and follow-up diamond exploration. Each sample comprised 20 to 30kg of -2mm material collected from heavy mineral trap sites.

Samples were processed and observed for diamonds and kimberlitic indicator minerals. A 0.175mm diamond and several chromites were recovered from Nolan Creek. Follow-up sampling did not return any additional diamonds. Microprobe analysis of the chromites suggested they were non-kimberlitic. The morphology of the diamond suggested it was synthetic in origin and probably had broken off a drill bit. Numerous chromites were recovered from 21 other areas. Microprobe analysis and follow-up sampling did not indicate a kimberlitic origin and no other indicator minerals were recovered. CRA concluded the chromites are probably of basaltic origin and that no further exploration for diamonds was warranted.

In 1987, Balmoral Resources NL entered into a joint venture with CRA Exploration. Balmoral Resources collected 85 bulk cyanide leach and -80 mesh stream sediment samples within the tenement area. The -80 mesh samples were analysed for Ag, As, Sb, Cu, Mn, Pb, Zn and Au. Following this survey, Balmoral Resources NL withdrew and was replaced by Australian Gold Resources Ltd in 1988.

Several significant gold anomalies were delineated, particularly from drainages in the vicinity of hills south of Bontaba Siding and also from areas farther south. Follow-up rock chip sampling over the anomalous region identified mineralised, gossanous quartz veins, altered porphyry and altered greywacke and quartzite with visible sulphide minerals. Five hundred and twenty-three rock chip samples were collected and analysed for Au and As. Fifty-three samples were analysed for Cu, Pb, Zn, Ag, Cd, Fe and Sb and 10 samples were analysed for W. Thirty-one samples were collected from rock outcrops where significant Au, Cu, Pb, Ag, As and Sb grades confirmed the stream sediment sampling results. Gold assay results ranged up to 7.8g/t and three samples returned >1g/t. The higher gold grades were interpreted as being related to narrow gossanous quartz veins.

A total of 6.6 line kilometres of ground magnetics was surveyed along five lines. Eleven reverse circulation percussion holes were drilled for a total of 618m at 52 Cranfield & Diprose four widely separated prospects distributed around the Bontaba Anomaly. Four hundred and one percussion chip samples were assayed but none of the drill samples returned >0.5ppm gold.

Australian Gold Resources withdrew from the joint venture in 1990. CRA then carried out a review of all exploration data. The breccia was identified as the most prospective unit but, considering the variable and generally low tenor of mineralisation at the surface, the region was not considered large enough to host a significant orebody. The Permit was relinquished in February 1991.

EPM 4026 ‘Herbert River’ was granted to CRA Exploration Pty Ltd in June 1985. The company targeted diamonds and diamond indicator minerals within a non-continuous 137km by 95km area that was designed to cover the north-eastern part of the Georgetown Province and adjoining Hodgkinson Province within the Bullock Creek, Ravenshoe, Tully, Cashmere, Kirrama and Valley of Lagoons 1:100 000 Sheet areas. This area was thought to be a likely provenance area for diamonds found in the O’Briens Creek gemfield.

Ninety-three stream gravel samples were collected and processed for analysis for kimberlitic indicator minerals. Twenty-nine samples were found to contain chromite and one contained a possible pyrope garnet. Nineteen samples had chromite grains that underwent SEM analysis and were all found to be non-kimberlitic in origin. The other chromite grains that were not analysed were also thought to be non-kimberlitic in origin after a comparison with the grains that were tested. The pyrope was thought to be of basaltic origin by analogy with the chromites found in the same sample.

The Permit was relinquished in August 1986.

EPM 4084 ‘Millstream’ was granted to Carpentaria Exploration Company Pty Ltd in September 1985. This Permit was taken up because of an internal 1972 MIM report of a heavy mineral sample from Weir Creek, 8km north-east of Ravenshoe, that contained ilmenite, chromite, rutile, magnetite, iron oxides, kyanite and zircon. The area was thought to have potential for kimberlites.

The company carried out petrological examinations of flow-banded rhyolites and Cainozoic basalt. A preliminary bulk sample was found to contain many black grains that were thought to be possible picroilmenite. They turned out to be rutile. The sample also contained three garnets, along with an abundance of sapphire, tourmaline and zircon. None of these minerals was kimberlite-related.

Although diamond exploration was not considered viable, further exploration was carried out for rutile. Chemical analyses of stream sediment samples (sieved to -2mmforICPPand-80meshforXRF)forCu,Pb,Zn,Bi,Sb,Mn,As,Ni,Co,Cr and Ti were carried out and demonstrated anomalous Ti west and north of Mount Fisher, linked mainly to basalt cover. Shallow auger drilling was followed by five deep auger holes that were drilled in areas with high Ti results. Material derived from the basalts assayed 1.5–2% Ti (ICP) to 3–4% Ti (XRF), 300–400ppm Cr, 30–60ppm Cu, 10–17% Fe and 150–250ppm (locally 400ppm) Ni. Holes that Queensland Geological Record 2008/04 53 bottomed in acid volcanics returned 0.2–0.2% Ti, <50ppm Cr, 10ppm Cu, 2–4% Fe and 10–20ppm Ni.

The Permit was relinquished in February 1986.

EPMs 8997 ‘Crystalbrook’ and 9120 ‘Crystalbrook West’ were granted to Poseidon Gold Ltd in September and December 1992, respectively. Poseidon targeted gold, copper, lead, zinc, silver and diamonds near Crystalbrook Homestead, 25km south-west of Chillagoe. EPM 8997 was centred on the Crystalbrook volcanic neck and EPM 9120 covered the northern margin of this intrusive.

These areas were considered to have potential to host bulk tonnage, low-grade gold and/or copper-gold deposits such as Kidston/Mount Leyshon style diatreme breccias, Red Dome style gold-base metal skarn and porphyry copper-gold deposits, and epithermal (and higher temperature) replacement and space-fill deposits, particularly in zones of structural preparation such as major structural intersections. The presence of appropriate intrusive rocks and tectonic setting, with Permo-Carboniferous high-level I-type intrusions and proximity to the Palmerville Fault, were critical components of the exploration model.

A secondary exploration target was diamond-bearing kimberlite or lamproite pipes. The reasons for assessing the project area for diamond potential were:

• Diamonds of unknown provenance have been reported from the O’Brien’s Creek gemfield to the south of the project area;

• The Palmerville Fault corridor represents a regional terrane boundary, with the project area falling on the cratonic side of the structure;

• Discrete dipolar magnetic features resembling the magnetic signatures of some known kimberlite or lamproite pipes were identified on aeromagnetic contour plots; and

• Previous diamond exploration in the project area had been of limited intensity, although possible kimberlitic chromite grains had been identified by CRA Exploration Pty Ltd within EPM 3982.

The project area covered six stratigraphic components, as defined by Best (1962) and Bultitude & others (1987):

• Dargalong Metamorphics — mid-Proterozoic mica schist, gneiss, granulite, pegmatite, granite, quartzite and amphibolite,

• McDevitt Metamorphics — mid-Proterozoic quartz-muscovite-garnet-cordierite schist, andalusite schist and quartzite,

• Cobbold Dolerite — Proterozoic dolerite, gabbro and amphibolite,

• Herbert River Granite — porphyritic biotite granite,

• Elizabeth Creek Granite — pink leucocratic granite, and 54 Cranfield & Diprose

• Crystalbrook Volcanic Neck — late Palaeozoic diorite.

In 1993, exploration comprised a literature review, collection and interpretation of airborne magnetic and radiometric data, broad-based drainage geochemistry (356 samples), targeted heavy-mineral drainage sampling, rock chip sampling and targeted heavy mineral sampling for diamonds. This work identified 15 anomalous drainage areas with >3ppb Au for follow-up assessment. Rock chip sampling (145 samples) indicated that the main mineralisation style in the area is small scale, auriferous, east- and north-east-trending, shear-hosted quartz-sulphide veins enriched in base metals. Two small occurrences (Silver Dollar and Hamil’s Hut) were farmed out to Saracen Minerals NL for further evaluation.

Thirteen heavy mineral stream sediment samples were processed for analysis for kimberlitic indicator minerals. Chrome spinel grains recovered from the samples were submitted for SEM analysis and were found not to be of kimberlitic origin. No further diamond exploration was carried out.

Gold and base metal exploration continued in 1994. Fourteen stream sediment samples were collected to follow up geochemically anomalous drainages. Assays results of 5.2–15.7ppb Au downstream of the Hamil’s Hut workings contrasted with results of 0.4ppb Au for the drainage above the workings. Forty-three follow-up rock chip samples were collected at Hamil’s Hut and analysed for Cu, Ph, Zn, As, Sb, Bi, Mo, Ag and Au. Multi-element results showed a strong correlation between Au and anomalous Bi (0.4–373ppm) and a correlation between Au and anomalous Mo (1.3–11.5ppm) plus Ag (<0.5–31ppm). In contrast, moderately to weakly anomalous As (3–240ppm) and base metals had a low degree of correlation with Au contents. Seventy-four soil samples from the Hamil’s Hut prospect returned up to 344ppb Au.

Two samples of gossans overlying structurally-controlled sulphide veins, hosted by shear zones in the McDevitt Metamorphics, were submitted for Pb–Pb dating. A late Palaeozoic (probable Permo-Carboniferous) age for the Pb in these occurrences precludes remobilisation from Proterozoic sediment-hosted massive sulphide deposits.

In 1995, rock chip sampling of mineral occurrences was carried out in conjunction with a geological mapping program. One hundred and ninety-one rock chip samples were assayed for Au, Cu, Pb, Zn, Ag, As, Mo, Sn, W, Sb and Bi. Four target areas — M1 (Pillar Mine section of the Silver Dollar Fault zone), M2, M3 and M8 (MBC group of workings) — were delineated.

Twenty-two rock chip samples of exposed lode material were collected along a 1300m strike length of the Pillar Mine (M1) section of the Silver Dollar Fault Zone. Eight samples returned 1.14–4.71g/t Au, with most of the remaining samples assaying 0.1–0.96g/t Au. Associated base metal, silver and arsenic contents were high. Twelve samples returned >1% Pb (1.08–11.6%) and 9–510ppm Ag. Fifteen samples returned >1% As (5.18–11.6%). Queensland Geological Record 2008/04 55

The eastern part of the Pillar Mine section of the Silver Dollar Fault Zone was check sampled. This sampling returned 0.189–1.61g/t Au, along with high Pb, Ag and As contents. A best result was 0.45m at 1.51g/t Au, 4.44% Pb, 160ppm Ag and 11.6% As.

Nine rock chip samples from the gossanous shear zone at M2 returned up to 3.94g/t Au. Most of the remaining samples assayed 0.17–0.74g/t Au. Sixteen rock chip samples were collected at M3. Four returned >1g/t Au (1.48–3.81g/t Au) and the other six assayed 0.1–0.59g/t Au.

Poseidon Gold sampled old workings and minor mineralisation at M4. The best results were from Sample 225790 (1.91% Cu, 1.84% Pb, 16.3% Zn and 162ppm Ag) and Sample 229027 (1.872% Cu, 4760ppm Pb, 9020ppm Zn and 198ppm Ag).

Three rock chip samples were collected at M5, two from across the vein and one selective sample of a bright red brown limonite veinlet. Highly anomalous arsenic and gold contents were found, along with some elevated base metal grades. Gold contents ranged from 0.611–0.712g/t and the maximum arsenic assay result was 1.73%.

Nineteen rock chip samples were collected from a set of locally gossanous, east-north-east-trending fracture zones. The best assay result was 4.21g/t Au, with 1.18% Pb, 1400ppm Zn, 21.2ppm Ag, 3150ppm As and 3100ppm Bi. Four other rock chip samples returned 0.14–0.48g/t Au.

At M7, a 0.25m wide sample of a gossanous vein in meta-arenites returned 2.12g/t Au, 2520ppm Cu, 2.12% Pb, 280ppm Ag and 1.69% As. Boxworked hematitic gossan float assayed 0.159g/t Au, 1.25% Cu, 7.01% Pb, 350ppm Ag and 3630ppm As.

Poseidon Gold collected 25 rock chip samples mostly from mullock and small stockpiles of untreated ore at M8, (MBC group of workings). Fifteen samples assayed >1g/t Au (1.12–3.51g/t). Five additional and check samples confirmed the auriferous nature of the gossanous quartz veining, with 1.83–5.64g/t Au.

Several old pits and a costean were found on a 150m section of a north-east-trending fault zone at M9. This zone is mostly in an amphibolite host rock. Nine rock chip samples were collected. Gold and arsenic contents were very low while seven samples returned Pb values >1%, ranging from 1.02% to 7.14% with corresponding silver values in the range of 4.4ppm to 111ppm. The best Pb value of 7.14% with 9710ppm Zn and 111ppm Ag related to a selective sample of quartz veined dump material hosting relict galena at site 701568. The rock chip sampling showed that Pb values >1%, extended into the wall rock. An example was site 701569 where a 1.8m wide channel of networked quartz veined, well fractured amphibolite gave Pb value of 1.02%.

Rock chip samples from M10 returned up to 1.7% Pb, 8350ppm Cu, 5430ppm Zn, 1090ppm Ag and 2.7% As from quartz-limonite veined dump material with malachite and cerussite. 56 Cranfield & Diprose

At M11, there are two caved shafts and two more recently excavated costeans on a north-east-trending mineralised structure that consists of 0.1–0.3m wide zone of siliceous breccia and siliceous, quartz-veined amphibolite that locally hosts banded crystalline quartz and chalcedonic quartz. Samples assayed up to 0.514g/t Au, 1.66% Pb and 74ppm Ag.

At M12 (Black Cockatoo Prospect), a 500m section of the Silver Dollar Fault Zone is characterised by extensive carbonate veining in intensively fractured and ferruginous dolerite in association with schist. One sample assayed 27.2g/t Au and 5750ppm Cu but the best result from follow-up sampling was 4ppb Au. The best result from nine additional and check rock chip samples was 10ppb Au and 156ppm Cu.

It was concluded that the Pillar Mine zone warranted further evaluation. Further exploration was proposed but was not carried out. Both Permits were relinquished in November 1995.

CROYDON AREA

EPMs 2872 was granted to Strategic Metals Corporation Pty Ltd in February 1981. The Permit was primarily acquired to evaluate anomalous combined Ta–Nb concentrations in fractured quartzite north of Prospect Homestead, 75km south of Croydon, and also to explore for fluorite and sedimentary uranium in Mesozoic sediments. The company’s attention was drawn to the area by the discovery of highly anomalous fluorine concentrations (21–31ppm) in groundwater in artesian bores in the region. Exploration subsequently focused on gold, platinum group metals and diamonds. Exploration was managed by Minplex Resources Pty Ltd.

In 1981, airborne magnetometry at 250m spacing was completed over an area centred near Prospect Bore. This survey delineated a south-east trending lineament and a strong residual magnetic anomaly at Prospect Bore. Water samples collected from Prospect and Lily bores assayed 20.1ppm F and 19.8 F, respectively. Uranium concentrations were only at background levels.

Two vertical core holes were drilled adjacent to Prospect Bore. They intersected Quaternary and Cretaceous sediments to depths of 57m, overlying fractured quartzite and porphyritic rhyolite with graphite inclusions. Basement samples assayed up to 144ppm Cu, 230ppm Zn and 185ppm Pb. Ta and Nb concentrations were only at background levels. As the drilling predated the airborne flying it was not sited to intersect the magnetic anomaly.

In 1982, the airborne magnetic anomaly was defined on the ground with a proton precession magnetometer survey at 25m by 100m centres. A well defined anomaly was delineated over a 600m length. Two percussion holes were drilled and established the anomaly as an ilmenite- and titanomagnetite-rich layered gabbro that averaged 15.15% Ti and 0.64% V2O5.

In 1983, a Landsat study was completed by Australian Photogeological Consultants to assist understanding of the relationship between groundwater Queensland Geological Record 2008/04 57 fluorine anomalies and regional lineaments. The Hailstone, Lily and Prospect Bore anomalies are clearly coincident with the Borer River Fracture Zone.

An airborne magnetic survey at 300m line spacing and 80m flight height was flown by Geoterrex Australia Pty Ltd over EPM 2872 and adjacent areas in November-December 1983. Interpretation of the survey results indicated that the gabbro drilled at Prospect Bore is one of a cluster of gabbro sills in the area. Magnetic modelling did not provide any orientation or geometry for these sills. A 6km diameter cauldron structure with a granite/granophyre core was interpreted to occur in the northern and central parts of EPM 2872.

In 1984, exploration shifted to a search for kimberlites, carbonatites, vanadiferous and titaniferous gabbros, and Olympic Dam style Cu–Au–U deposits. Ground studies included gridding and ground magnetic surveys over a carbonatite-type aeromagnetic anomaly and a gabbro-type anomaly 2km south-east of Lily Bore.

A rotary-percussion hole, drilled to 136m to test the carbonatite anomaly intersected sericitised and carbonatised, magnetic gabbro from 96–136m.

Twenty-one samples were assayed for Co, Mn, Cu, Pb, Sn, Ni, Cr, V2O5,Asand TiO2. No anomalous concentrations were detected. Petrological examination of samples indicated that the rock is a two pyroxene gabbro in which the pyroxene has been uralitised. It contains normal abundances of opaque minerals, with magnetite and ilmenite being the most abundant. Rare pyrite and chalcopyrite were also observed.

Strategic Minerals Corporation then took up adjoining EPM 3647 in May 1984. This Permit covered the Plain Bore area, 60km south-west of Croydon, where the aeromagnetic survey had delineated a number of anomalies that were interpreted as possible carbonatite and kimberlite bodies. A ground magnetic survey was carried out over the strongest of the potential kimberlite anomalies, which had been interpreted as a pipe-like body of low magnetisation, consistent with a kimberlitic or lamproitic intrusion at ~80m depth. Drill testing was delayed by unfavourable weather conditions.

In 1986, exploration was taken over by Golden Plateau NL under a joint venture agreement. Ground magnetic surveys were carried out over selected anomalies in EPMs 2872 and 3647 prior to site preparation for drilling. Eight percussion holes, totalling 886m, were drilled. Three holes were sited on anomalies interpreted as possible kimberlites; two holes were sited on anomalies interpreted as gabbros; two holes were on carbonatite anomalies; and the other was drilled to further evaluate the layered gabbro previously drilled near Prospect Bore. Two probable kimberlite holes were abandoned before intersecting basement. The third hole intersected Proterozoic micaceous schists at 108m depth. The source of the magnetic anomaly was not intersected before the hole was terminated at 132m. One gabbro anomaly was confirmed but no significant mineralisation was intersected. Proterozoic? rhyolite (?Croydon Volcanic Group) was intersected at the other ‘gabbro’ anomaly. One hole at a ‘carbonatite’ anomaly was abandoned due to drilling difficulties. The other hole intersected non-magnetic Proterozoic granite at 126m. 58 Cranfield & Diprose

High Ti contents were not duplicated for the gabbro near Prospect Bore. However, platinum and palladium were anomalous, with platinum increasing down the hole to a maximum of 0.06ppm at the base. Palladium showed a similar increase to a maximum of 0.025ppm in the 96–98m interval.

EPMs 4429, 4785 and 4786 were granted to Strategic Mineral Corporation in September 1986 and June 1987. An aeromagnetic survey was flown over EPMs 4785 and 4786 by Austirex International Ltd in February to August 1987. No other exploration was reported before EPM 2872 was relinquished in February 1987 and EPMs 3647, 4429, 4785 and 4786 were conditionally surrendered in favour of EPM 4853 in August 1987.

EPM 3620 was granted to Strategic Minerals Corporation NL in December 1983. The Permit covered the Hailstone Bore area, 55km south-west of Croydon. High fluorine concentrations in groundwater in this area indicated potential for kimberlite, carbonatites hosting niobium and copper mineralisation, tin granites and Olympic Dam style Cu-Au-U deposits. An aeromagnetic survey delineated four anomalies that were interpreted as possible carbonatite bodies.

A field reconnaissance was carried out to determine suitable areas for a drilling program. Drilling in adjacent EPM 2872 demonstrated that a similar anomaly was due to gabbro and not to carbonatite. The aeromagnetic data were reassessed and it was concluded that the anomalies were most likely to be due to gabbro bodies at depths of ~200m. Consequently, the Permit was relinquished in August 1985 without carrying out any drilling.

EPM 3805 was granted to Strategic Minerals Corporation NL in September 1984. This Permit, 55km south-west of Croydon, covered the south-east extension of the major Borer River Fracture Zone and the fringes of several aeromagnetic anomalies in adjacent EPM 2872. The only work carried out was a general field reconnaissance to determine suitable areas for drilling. An assessment of drilling results in EPM 2872 downgraded the economic potential of the aeromagnetic anomalies and EPM 3805 was relinquished in August 1985 with no further investigations.

EPM 3806 was granted to Strategic Minerals Corporation NL in September 1984. This Permit, 55km south-west of Croydon, covered the south-east extension of the major Borer River Fracture Zone and the fringes of several aeromagnetic anomalies in adjacent EPM 2872. The only work carried out was a general field reconnaissance to determine suitable areas for drilling. An assessment of drilling results in EPM 2872 indicated that a titaniferous layered gabbro in EPM 2872 extends into EPM 3806. However, because only a small part of the interpreted extent of this intrusion extended into the Permit, EPM 3806 was relinquished in August 1985 with no further investigations.

Queensland Metals Corporation NL was granted EPM 4012, 150km south-west of Croydon, in May 1985 and undertook exploration for carbonatites and kimberlites based on a very large fluorine hydrogeochemical anomaly within the Carpentaria Basin from water bore data. Queensland Geological Record 2008/04 59

A gravity survey was carried out over the tenement and an analysis of the results showed that it defined a zone of anomalous gravity that may be an expression of dense remnant sediments of a failed rift system. A water bore in this area intersected sulphides in sedimentary basement rocks but the details were not well documented. The company planned to re-drill this bore.

Two holes were drilled in October–November 1986. One hole intersected a basement sequence of fine sediments overlying very altered microgabbro. The second hole intersected basement metasediments with quartz veining. The main aquifers were fracture zones in the basement rocks, but the groundwaters were not enriched in fluorine. Overall, the exploration in this permit failed to identify the source of the anomalous fluorine levels and the Permit was relinquished in February 1987.

EPM 4853 was granted to Strategic Minerals Corporation NL and Strategic Metals Corporation NL in August 1987. This permit replaced EPMs 2872, 3647, 4429, 4785 and 4786, in which exploration had delineated a number of geophysical anomalies, one of which proved to be a titanium- and vanadium-rich gabbroic intrusion. Exploration subsequently focused on gold, platinum and diamonds. Exploration was carried out by Golden Plateau NL as operator and manager under a joint venture agreement.

Percussion and core drilling were carried out to test the Prospect Bore anomaly and a number of other aeromagnetic anomalies. Twenty-six percussion holes were completed for a total of 211 m and 18 holes were extended by core drilling for an additional 933m.

Three holes at the Prospect Bore anomaly all intersected a variably hydrothermally altered, titanium-rich layered gabbro underlain by quartzite. Platinum contents ranged from <0.01–0.04g/t, with grades of up to 0.38g/t over a one metre interval. Isolated samples with epithermal quartz-carbonate veins returned grades of up to 0.68g/t Au over a one metre interval. No diamonds were found.

Drill holes at the other anomalies intersected gabbro, felsic volcanics, intrusive felsic volcanics, and graphite-rich breccia. The gabbros all had combined precious metal contents consistently in the range 0.02–0.08g/t. No significantly anomalous precious metal contents were found in the other rock types.

Golden Plateau withdrew from the joint venture in 1989. Strategic Minerals was unable to find a new joint venture partner and relinquished the Permit in August 1989.

GEORGETOWN AREA

EPM 3886 was granted to CRA Exploration Pty Ltd in November 1984. The Permit was taken up to cover Cawana Lake, a geomorphological anomaly in the north-eastern corner of the Georgetown 1:100 000 Sheet area that probably formed by the damming effect of a tongue of Tertiary McBride Basalt. Because of 60 Cranfield & Diprose its proximity to the alluvial diamonds found in Elizabeth Creek north of Mount Surprise, the lake which was postulated to represent a kimberlite.

In early 1985, one loam sample was collected from the centre of the lake. This sample was found to contain 11 grains of basalt-derived chrome-spinel. The lake then filled with water preventing further work.

Four and a half line kilometres of reconnaissance ground magnetic traverses were completed across the dry lake bed. Strongly anomalous responses were detected over the McBride Basalt to the south and west of the lake. A number of weak responses were recorded in the centre and towards the lake edges.

The chromite grains from the 1985 sampling were sent for microprobe analysis. The results showed that all the grains were low chromium spinels and not kimberlite-related. Nine shallow auger holes were drilled for a total of 54m, all ending in pale green, friable, weathered basalt. A sample from the bottom of each hole was processed for kimberlitic indicator mineral analysis. Results were not finalised at time of the final report. CRA concluded that the lake is not related to a kimberlitic structure and relinquished the Permit in February 1987.

EPM 8792 ‘Cawana Lake’ was granted to Snowmist Pty Ltd and JT Kruckow in June 1992. The targets were diamonds, tin, tungsten and rare earth elements in the Cawana Lake area, on the south-east margin of the Namarrong Cauldron Complex north-east of Georgetown. Snowmist carried out a geological reconnaissance, ground magnetic surveys, rock chip and stream sediment sampling, pan concentrate sampling, petrographic studies and literature research. None of the stream sediment samples returned any kimberlitic indicator minerals. Significant areas of greisenised granite were found to contain anomalous tin mineralisation. Although none of the target minerals were found in economic quantities, the company retained the Cawana Lake area because it represents a large topographic and geological anomaly that suggests the presence of diatreme rocks.

A small number of samples were collected from Cawana Lake and sent for analysis for kimberlitic indicator minerals, but none were found. The Permit was relinquished in June 1994.

MOUNT SURPRISE AREA

EPM 1692 was granted to CRA Exploration Pty Ltd in November 1976. Although the Permit did extend into the north-eastern corner of the Georgetown 1:100 000 Sheet area, most of the tenement area was within the Red River, Atherton and Einasleigh 1:250 000 Sheet areas. Exploration focused on a search for diamonds following unconfirmed reports of diamonds as large as 1.8 carats being found in the O’Brien’s Creek topaz field north of Mount Surprise. Two stones reportedly from O’Brien’s Creek were tested and found to be diamonds of gem quality.

A helicopter-borne drainage sampling program was carried out. Fifty-two pan-concentrate and -80 mesh samples were collected within an area of 320km2, mainly within the Atherton 1:250 000 Sheet area. Queensland Geological Record 2008/04 61

Nine samples contained possible kimberlitic indicator minerals (garnet and ilmenite). However, microprobe studies of garnets suggested a metamorphic origin. ‘Ruby tin’ was found in many of the samples. Geochemical results were interpreted as indicating poor potential for both kimberlite and base metals. Uranium prospectivity was also considered to be poor. Anomalous niobium levels were attributed to columbite/tantalite in pegmatites. Base metal anomalism in stream sediment samples from an area of Warby Volcanics in the Atherton 1:250 000 Sheet area was considered to warrant follow-up, but no further work was reported. The Permit was relinquished in February 1977.

EPM 1693 was granted to CRA Exploration Pty Ltd in December 1976. This Permit was contiguous with EPM 1692. The company collected 66 bulk stream sediment samples. Twenty samples contained possible kimberlitic minerals. However, the garnets were of a uniform colour, indicating that they came from metamorphic rocks or granite/pegmatite sources. Electron probe analysis identified the garnets as spessartite, almandine and grossularite, none of which are kimberlitic in origin. Geochemistry samples were also collected to determine if kimberlite source rocks occur in the area. Chromium assays were uniformly low, whereas niobium and titanium results varied with no obvious correlation. Also, there was no obvious correlation between areas that had possible kimberlitic indicator minerals and anomalous niobium and titanium. Radiometric counts were measured at each site but nothing significant was indicated by the results. The Permit was relinquished in February 1977.

EPM 2176 was granted to Houston Oil and Minerals Australia Incorporated in September 1979. The company explored a system of Cainozoic stream gravels, parallel to the present-day Einasleigh River and Elizabeth Creek, that were considered to have potential for palaeoplacer tin and diamond deposits.

An area near the eastern end of the Permit was selected for detailed examination and some 16.5km of seismic refraction surveying was carried out to define palaeochannel profiles and stratigraphy. Bulk samples of alluvium were obtained by costeaning and Calweld bucket drilling at selected sites. Concentrates were assayed for tin, gold and tungsten but yielded low grades. Two 100t samples, representing upper and lower gravel zones from a costean, assayed <340g/t Sn and <10g/t Sn, respectively. A considerable amount of topaz was recovered.

The bulk samples were also analysed for diamonds and kimberlitic indicator minerals; none were found. The palaeoplacer system was concluded to have no association with the diamonds found by fossickers in the O’Brien’s Creek area.

The Permit was relinquished in January 1982.

EPM 2556 was granted to Houston Oil and Minerals Australia Incorporated in August 1980. This permit comprised three sub-areas covering parts of the Georgetown 1:100 000 Sheet area and the Einasleigh and Red River 1:250 000 Sheets. The Permit was explored for palaeoplacer deposits of tin and diamonds in conjunction with EPM 2176, which was in the Red River 1:250 000 Sheet area. The main part of the permit covered the older alluvial deposits of the Einasleigh 62 Cranfield & Diprose

River upstream of EPM 2176. Two smaller parts of the Permit flanked EPM 2176 near its north-western margin.

The bulk of the palaeoplacer deposits occur as deep lead deposits beneath flows of the Undara Basalt of the McBride Basalt Province. No significant exposures of gravel were found during a thorough ground inspection of the Mount Surprise area. One drill hole intersected 24m of basalt and 2m of gravel. Seismic and resistivity methods could not be used due to interference caused by the overlying basalt flows. A program of closely spaced drilling would be required to locate any buried channel deposits. Because of the envisaged exploration and mining difficulties stemming from the substantial basalt cover, the permit was relinquished in June 1981.

EPM 3973, which covered large parts of the Red River, Atherton and Einasleigh and a small part of the Georgetown 1:250 000 Sheet areas, was granted to CRA Exploration Pty Ltd in December 1984. Regional geological investigations had suggested potential for hard rock sourced diamonds in the north-eastern part of the Georgetown Province.

In 1985, two hundred and twenty-eight drainage gravel samples were collected and processed for analysis for diamond indicator minerals. No diamonds or indicator minerals were recovered. Chromite and pyrope occurrences were attributed to a Tertiary basaltic source after SEM analyses had been carried out on a selection of chromite grains.

Fifty-one samples were collected in 1986 and processed for analysis for kimberlitic indicator minerals. Chromite was found in eight of these samples, and SEM analysis indicated that these were probably basaltic in origin. It was concluded that no further exploration for diamonds was required.

A review of literature pertaining to the Permit area highlighted an untested Cu–Pb–Zn stream sediment anomaly in the Fever and Ague Creek area (Einasleigh 1:250 000 Sheet area). Subsequent exploration located base metal-bearing gossans associated with several stratiform quartz-gahnite lodes that extend over a strike length of >6.5km. Detailed mapping, rock chip, stream sediment and soil sampling, and ground magnetics surveys were carried out and five percussion holes (totalling 532m) were drilled at the Reisling Prospect. Assay results were disappointing; with the best intersection being 4m at 1.3% Zn. High Pb contents recorded for surface samples were found to be attributable to surface enrichment; primary mineralisation carried <1000ppm Pb.

A helicopter-based stream sediment survey was carried out over the Einasleigh 1:250 000 portion of the tenement to search for extensions to the known base metal mineralisation and for new zones, without success. Samples were also collected for cyanide leach analysis for gold. A SIROTEM survey conducted over the known zone of base metal mineralisation failed to show any typical massive sulphide conductor response and work on this zone was curtailed.

The cyanide leach survey yielded several significant anomalies, most of which were downgraded by follow-up sampling and analysis. One catchment with Queensland Geological Record 2008/04 63 repeatable anomalous gold assay results was found to contain a slightly gossanous quartz vein. Rock chip samples from the vein assayed 0.04–0.08ppm Au. No significant potential was considered to exist for economic gold mineralisation and the Permit was relinquished in September 1987.

EPM 4064 ‘Fulford Creek’, 55km north of Mount Surprise, was granted to CRA Exploration Pty Ltd in August 1985.

Fourteen stream sediment samples were processed for analysis for kimberlitic indicator minerals. No diamonds were found. Chromite was found in eight samples. Microprobe analysis of four chromite grains determined them to not be of kimberlitic origin. The permit was relinquished in December 1985.

EPM 8991, ‘Bonnor Knob’, 25km north-west of Mount Surprise, was granted to CRA Exploration Pty Ltd in September 1992. The area was under Restricted Area 95 from 1979 to 1992 and was considered to be underexplored for gold mineralisation. Diamonds were also a target but no actual diamond exploration was reported.

The tenement covered an area of Proterozoic metamorphic rocks and granites, Silurian metamorphic rocks and granitoids, Carboniferous granites and volcanic rocks and Cainozoic basalts. It contains numerous alluvial tin occurrences and surrounds the O’Brien’s Creek gemfield, which is a significant producer of topaz, aquamarine and other semi-precious stones. These are worked by prospectors from alluvium, colluvium and eluvium and are thought to be derived from veins and greisens in the Elizabeth Creek Granite. Small diamonds have been recovered with the semi-precious stones from gravels in the O’Brien’s Creek area and by tin miners along Elizabeth Creek. Alluvial and eluvial tin have been worked along Six Mile, Nine Mile and Elizabeth Creeks.

One hundred and seventy-one -80 mesh stream sediment and 59 rock samples were collected to follow up areas considered anomalous from previous exploration. A magnetite-bearing granite dyke in metamorphic rocks at the North Insulator Creek Prospect assayed 0.6% Cu and 0.4ppm Au. Float samples of narrow quartz-mica-magnetite greisen veins assayed up to 0.5% Pb, 0.2% Zn, 0.1% Sn, 1.2% As and 0.3% Cu. Stream sediment samples assayed up to 0.18ppm Au, 1.1ppm Ag, 8500ppm As, 1.85ppm Bi and 4850ppm Cu. Several follow-up samples at the Scrape Creek Prospect had elevated gold that correlated with high tin grades. Samples from an area of Carboniferous granite at Six Mile Creek were elevated in As, Bi, Cu, Pb, Zn, Cd and Mo. Greisen veins similar to those at North Insulator Creek and quartz-veined granites were noted in float in several catchments. Samples from Nine Mile Creek were anomalous in Cu, Bi and As. Alluvial tin mining has been reported in Nine Mile Creek itself and minor greisen veining was noted when traversing upstream from the sampling sites. The Bonnor Creek West Prospect consisted of Carboniferous granite with elevated Au in -80 mesh stream sediment samples, but the source of the gold was not clear. Several samples from the Flaggy Creek area were elevated in gold but follow-up samples generally returned disappointingly low gold contents. The Twelve Mile Range South Prospect is on the edge of the Warby Ring Complex, a Carboniferous rhyolite complex within Carboniferous granites and minor remnants of 64 Cranfield & Diprose

Proterozoic metamorphic rocks. Samples from here were anomalous in Cu, Au and Bi. A sample of boulders of vughy quartz-sericite greisen assayed 2.6% Sn and 0.1% W.

Greisen veining was noted in float samples of coarse-grained quartz-phyric granite porphyry at two localities. The greisen bodies are thin (100–300mm wide), trend 310° magnetic and dip vertically. The largest coherent body is a 10m wide rubbly outcrop with a discontinuous 50m strike length giving way to thin quartz veins with subordinate greisen to the north-west and terminating abruptly in barren granite to the south-east. Channel and rock grab samples assayed up to 1810ppm Sn and 57ppm W.

Exploration in the Twelve Mile Range South area indicated anomalous tin that was considered to be due to minor greisen veining and unlikely to meet the company’s target size. The Permit was relinquished in June 1996.

EPMs 9287 ‘Mount Surprise’ and 9979 ‘Gallowary’ were granted to Northern Diamonds Pty Ltd in May 1993 and April 1994, respectively. The tenements were centred on the Einasleigh River on Van Lee Station, ~80km north-west of Mount Surprise. Exploration targeted gold and diamonds between Martin and Parallel Creeks.

In 1993, Northern Diamonds carried out air photo interpretation, ground studies and reviews of previous exploration results to identify palaeoplacer leads that might contain diamonds. Broader studies of the geomorphology of the Elizabeth Creek and Einasleigh River drainage systems were carried out to provide pointers to the source of diamonds recovered in the Elizabeth Creek area. It was concluded that all the diamonds discovered had come from a 50km long relict Cretaceous palaeoplacer paralleling Elizabeth Creek. Five bulk samples were collected from alluvium in and adjacent to the palaeoplacer. Concentrates containing cassiterite, ilmenite, garnet, monazite, zircon, gold, sapphire and topaz were sent to Belmont Laboratories in Western Australia for assessment. One diamond was recovered from the >1mm fraction.

Two possible kimberlite pipes were examined during a helicopter survey. One anomaly on the eastern side of the Einasleigh River was identified as a dacitic explosion vent area in the Galloway Volcanics. The other anomaly, north of Parallel Creek, was covered by Cretaceous gravels.

Cyprus Gold Australia Corporation entered a joint venture agreement with Northern Diamonds in December 1994 and took over management of the exploration, targeting bulk tonnage, low-grade gold mineralisation. Two possible source areas of gold anomalism were outlined by bulk cyanide leach stream sediment sampling. These areas were followed up by detailed stream sediment sampling (130 samples), regional soil lines and rock chip sampling.

A series of tributaries draining from the west into Dixons Creek, south of Black Soil Dam were anomalous in Cu, Mo, Ag, As, Sb and Pb, with an apparent outer halo of Bi, As and Pb. The highest gold assay result was 5ppb Au. Ten rock chip Queensland Geological Record 2008/04 65 samples were collected at Black Soil Dam, but returned no significant results other than one assay of 0.1ppm Au.

A second area of anomalism was located in the vicinity of Jape Creek, 4km north of the Queeko tin mine. Stream sediment samples assayed up to 37ppb Au, l6ppm Bi, 20ppm Cu and 13ppm Pb. Follow-up BCL stream sediment sampling and widely spaced soil sampling were collected to locate the source of the anomalous gold. Twenty-seven rock chip samples were collected, mainly from outcrops adjacent to stream sediment sample sites. No hard rock source for the gold could be established.

One hundred and thirteen RAB holes were drilled at Jape Creek and Black Soil Dam and 23 RC holes were drilled at Jape Creek to test for mineralisation in granite and porphyries below the sandstone-granite unconformity. No anomalous gold was detected. EPMs 9287 and 9979 were relinquished in May 1996 and April 1996, respectively.

GREENVALE AREA

EPMs 3412, 3413, 3414 and 3415 were granted to CRA Exploration Pty Ltd in March 1983 and formed the Cheviot Hills Project. CRA explored for possible kimberlitic occurrences in the headwaters of the Stawell River (mainly in the Chudleigh Park 1:100 000 Sheet area). The project was based on reports of diamonds found near the Hann Highway. Very high variations in magnetism were due to basalt cover in the area and the survey proved ineffective for producing targets based on magnetic anomalies. Some anomalous readings were obtained from areas where the basalt cover was minimal but ground magnetic surveys indicated that they were not due to a kimberlitic source. No further work was considered to be warranted and the Permits were relinquished in June 1983.

EPMs 3463, 3464 and 3660 were granted to Cultus Pacific NL and Southern Ventures NL in May 1983 and May 1984. The target was uranium mineralisation in the Lyndhurst Homestead, Pages Swamp Creek and Lava Creek areas. Twenty-five percussion holes were drilled to the north and south of Oak Park Homestead at spacings of 3 to 7km. Each hole was logged with a SP probe and water samples were analysed for uranium. No anomalous uranium was detected in any of the water samples.

The companies also examined the potential for kimberlitic indicator minerals in the sedimentary rocks. Heavy mineral fractions from drill cuttings were petrologically examined. Much chrome diopside was recovered from the samples but, without any other indicator minerals, it was concluded that the chrome diopside was probably from a non-kimberlitic source. The aluminium content was higher than would be expected for chrome diopside from a kimberlitic source.

The Permits were relinquished in May 1985.

WJ and IG Croker were granted EPM 4707 in April 1987. The target was alluvial and hard rock gold in the Broken River area (Burges 1:100 000 Sheet area). The holders 66 Cranfield & Diprose tested for alluvial gold and collected rock chip samples from outcrops and costeans at the Wally’s Hope, Janelle’s Hope and Becky’s Hope Prospects. Anomalous gold contents were recorded for all these prospects.

Stream sediment testing was carried out at six locations along the Broken River. Samples were examined by electron microscope scanning and 5kg samples were collected for examination by Pilbara Laboratories. Bulk samples were processed through an alluvial gold testing plant. Gravel from an area of Tertiary basalt (Test No. 113) contained sapphire, zircon and gem quality garnet. Black spinel was abundant but not of gem quality. Cinnabar was the dominant mineral in the area.

In 1989, Newmont Australia Ltd entered into a joint venture with the Crokers and carried out a detailed -3mm BLEG drainage survey comprising 353 stream sediment samples and 200 composite outcrop or float rock chip samples. Eight stream sediment anomalies with >1ppb Au were delineated, enclosing the Wally’s Hope – Maggie May, Janelle’s Hope, Drizzle, Becky’s Hope and Rabbit Flat Prospects. Follow-up work in 1990 focused on Wally’s Hope – Maggie May and Janelle’s Hope and comprised detailed mapping, rock chip and soil sampling, costeaning, ground magnetic and IP surveys and scout percussion drilling. Newmont had an option agreement over eight mining claims held at Wally’s Hope. Percussion holes intersected patchy zones of low-grade gold mineralisation, with a best result of 3m at 3.2g/t Au. Newmont attempted to define a resource at Janelle’s Hope but soon withdrew from the joint venture.

Newmont analysed heavy mineral concentrates for kimberlitic indicator minerals in 1989. Results are still confidential.

A consultant carried out a review of the tenement area for its limestone and marble potential for Broken River Marble Pty Ltd in 1992.

Ownership of the Permit was transferred to AS Marton and Associates in December 1995, who entered into a joint venture with Werrie Gold Ltd in November 1996. Resource drilling was completed at 10m spacings on 20m lines at Maggie May (ML 10152), targeting a 0.1ppm Au soil anomaly. The deposit proved to be uneconomic for the nearby Big Rush plant.

EPM 4707 is currently held by Queensland Epithermal Minerals Ltd. Exploration results, except for those given in relinquishment reports, are confidential.

EPMs 9174, 9910 and 10076 were granted to Poseidon Gold Ltd in February 1993, February 1994 and May 1994, respectively. These Permits formed the Poison lake project. The area was taken up to follow up intersecting geological and geophysical structures and aeromagnetic anomalies in an area north of Greenvale that is partially covered by Tertiary sediments on the western margin of the Camel Creek Subprovince of the Broken River Province. The target was gold mineralisation.

In 1993, processing of aeromagnetic data confirmed two major reversely polarised magnetic anomalies and identified another four smaller negative anomalies along north-west-trending structures that cut across the dominant Queensland Geological Record 2008/04 67 north-north-east-trending basement stratigraphy. Regolith mapping in 1994 indicated that the anomalies are masked by early Tertiary sediments. The anomalies could represent mafic plugs or stocks, magnetite-bearing skarns, magnetite-bearing alteration pipes above intrusions, or kimberlite pipes with diamond potential.

Ground magnetic surveys were carried out over four anomalies in 1995 and eight holes (367m reverse circulation and 54m core) were drilled at five anomalies. Drilling showed that the magnetic anomalies are unlikely to be due to a kimberlitic source. A bulk soil sample and samples taken from the drill holes were processed for kimberlite indicator minerals. No kimberlitic indicator minerals were recovered.

A hydrothermal breccia was intersected at one prospect and anomalous Au and base metals were intersected at another, as well as a potential mineralised magnetite skarn. Follow-up exploration downgraded the potential for economic gold mineralisation in the area. EPM 9910 was relinquished in December 1996 and EPMs 9174 and 10076 were relinquished in March 1999.

RICHMOND–HUGHENDEN AREA

EPMs 2057 to 2060 were granted to Houston Oil and Minerals Australia Incorporated in January 1979. The area was selected based on a report that diamonds had been found near the headwaters of the Einasleigh and Gilbert Rivers, in the Richmond-Hughenden area. Regional stream sediment sampling for kimberlite indicator minerals was carried out over a 7500km2 area covering Maiden Spring Creek and Lake Gilbert.

One hundred and forty-eight samples were collected at a density of one sample per 50km2. All samples were analysed for indicator minerals; 190 grains were sent for examination by electron microprobe analysis. No indications of a possible diamondiferous kimberlite were found. The Permits were relinquished in May 1979.

WINTON AREA

EPP 279, 150km south-west of Winton, was granted to Crusader (Mawson) Pty Ltd (30%), Abrolhos Oil & Investments Ltd (10.86%), Bridge Oil Ltd (14.28%), Minora Resources NL (11%), Cornwall Group (16.85%), Lennard Oil (10%) and Laurel Bay (7%) in August 1980. Saracen Minerals NL managed the exploration program.

Three topographic anomalies were located within the tenement from interpretation of air photos and Landsat imagery. Surface material was collected from each anomaly and stream sediment samples were collected where appropriate. No indications of kimberlitic indicator minerals were found at any of the anomalies. The Permit was relinquished in September 1991. 68 Cranfield & Diprose

BOULIA AREA

EPMs 4206 and 4207 were granted to CRA Exploration Pty Ltd in February 1986. These permits formed the Beattie Creek project, on the Queensland–Northern Territory border 200km west of Boulia, and were taken up to cover detrital occurrences of possible kimberlite indicator minerals,

Regional stream gravel samples were collected and processed for analysis for kimberlitic indicator minerals. A number of samples contained chromite and picroilmenite grains that could potentially be of kimberlitic origin. Similarities in the morphology of the chromite and picroilmenite grains indicated a common source. Five samples were linked back to a conglomerate source. Chromites and picroilmenites grains from another area were determined to be possibly from a kimberlitic source. The source of the remaining samples was unknown. Rock chip sampling returned negative results for indicator minerals.

It was concluded that, without finding any diamonds, any kimberlitic source in the area would not be significant and no further work was warranted. The Permits were relinquished in November 1987.

BEDOURIE AREA

EPMs 15471 to 15479 were granted to Ausquest Ltd in March 2007. This block of tenements formed Ausquest’s Diamantina Project and covered an area between Bedourie and Birdsville in south-west Queensland. The company was targeting magnetic anomalies that could reflect a new kimberlite province near the south-eastern margin of the North Australian Craton.

Airborne magnetic and radiometric data were reviewed but no magnetic anomalies of interest were located. No field work was carried out within EPMs 15471 and 15473 to 15479 before they were surrendered in April to October 2007. EPM 15472 is current and exploration results for this permit are confidential.

DIRRANBANDI AREA

EPM 14661 was granted to Regional Exploration Management Pty Ltd, a wholly-owned subsidiary of Diatreme Resources Ltd, in November 2004.

A review of all available data was carried out and a geological interpretation utilising air photos and satellite imagery was completed and followed by field checking. The company identified about 20 circular topographic depressions with potential to be diamondiferous diatremes in an area 50km north-west of Dirranbandi.

Ground magnetic traverses were carried out over two of these anomalies and showed weak magnetic lows, consistent with volcanic maars. Seven bulk samples collected from drainage systems were found to contain garnet. Petrological Queensland Geological Record 2008/04 69 examination indicated that at least one of the garnets originated from a basaltic carrier magma formed under ultrahigh pressure.

The company intended to carry out drilling on two of the targets but depths and conditions were unknown and a decision was made to not proceed. The Permit was relinquished in October 2006.

EPMs 2490 and 2513 were granted to Oilmin NL (50%), Transoil NL (25%) and Petromin NL (25%) in July and August 1980, respectively. Exploration focused on scattered circular depressions (up to 1.5km diameter) in the Dirranbandi area as potential diamond-bearing kimberlites.

In 1980, air photo and ground magnetic surveys were carried out to delineate any anomalies. Rotary holes were drilled to test a number of topographic depressions. No kimberlites or intrusive rocks were intersected, but the heavy mineral fraction from fine, yellow-green sands contained pale orange-pink pyrope and picroilmenite. Probe analyses showed that the pyrope falls in cluster group 3 of Dawson & Stevens (1975), which is dominated by pyrope from an eclogitic source. The orientations of the depressions indicated a strong north-north-east structural control, suggesting affinities with the Darling Lineament. The depressions may be collapse structures. There is potential for a kimberlitic source nearby but not the closest basement rock outcrops.

An aeromagnetic survey was flown in May and June 1982, but no anomalies were detected. The companies concluded that no further exploration was warranted and the Permits were relinquished in June and July 1982.

EPMs 7224 and 8281 were granted to Metallurgical Refining and Development Company Pty Ltd in June and October 1990, respectively and formed the company’s Dirranbandi diamond project. The permits were applied for based on the apparent structural location of the Darling Lineament, the Grafton Lineament and a tectonic mobile zone.

A soil sampling program was carried out in 1990/91 and samples were processed for analysis for kimberlitic indicator minerals and geochemistry. Pyrope garnets and picroilmenites were recovered. Aeromagnetic data were interpreted and a drilling program planned.

Four bulk samples were collected in 1991/92 and processed for analysis for kimberlitic indicator minerals. Chromite grains from these samples were sent for microprobe analysis, but initial results were not favourable for a kimberlitic source. However, the number of samples was small and the results were not conclusive. Additional samples were collected and forwarded for analysis. Two drill holes were completed to test two aeromagnetic anomalies. Neither drill hole reached the target depth and no kimberlitic rocks were intersected.

Bore water geochemistry was studied, especially elements known to be associated with kimberlitic sources, such as Zr, Ba, Sr, F and P. The K:Na ratio was also evaluated. Results indicated a possible connection to a kimberlitic source and it was recommended that drilling be carried out. 70 Cranfield & Diprose

Several holes drilled in 1992/93 reached the target depth. Drill core was analysed to determine if there was a possibility that the rocks were from a kimberlitic or lamprophyric source. The geochemistry was found to not be similar to other known kimberlitic or lamprophyric sources. Core samples were also sent for analysis for kimberlitic indicator minerals. A synthetic diamond was found in one sample. No kimberlitic indicator minerals were found in any of the samples.

In 1993/94 drill core from two holes was confirmed as having intersections of lamprophyric material. Chromite grains were found to be kimberlitic in origin. Further exploration of this area was noted as necessary to determine the potential to discover diamonds in this area. Stratigraphic and seismic interpretation did not identify any other areas with potential for diamond-bearing rocks. Previous drilling in areas of circular depressions did indicate the presence of volcanic pipes but the drill core did not indicate that they were diamond-bearing.

The exploration results were reviewed in 1996. No further work was recommended and the EPMs 7224 and 8281 were relinquished in June and September 1996, respectively.

ROLLESTON AREA

EPM 4956 was granted to Bernard Exploration NL in September 1987. Exploration was carried out by CRA Exploration Pty Ltd under a joint venture agreement.

Ground magnetic surveys (16.3 line kilometres) were carried out over four pan-like geomorphic features in Tertiary sediments that could reflect underlying kimberlite pipes in an area south-east of Rolleston. A magnetic source was partly coincident with two of the anomalies. Thirteen loam samples were collected from the four anomalies and three other targets to the north-east. Chrome spinels were found in samples from all but one of the seven targets sampled. The morphology of these grains suggested a basaltic source indicating basaltic rocks as the source of the magnetic anomalies. Soil geochemistry returned lower Nb values than expected, but this was attributed to dilution in an inward drainage.

Three percussion holes were drilled at three targets and intersected a sequence of sediments and basalt. Magnetic susceptibility readings were taken at regular intervals. Fifteen samples from the drill holes and surrounding areas were sent for analysis. The results did not indicate a kimberlitic origin. It was concluded that the clay pans are due to normal geomorphic processes. The Permit was relinquished in December 1988.

MOUNT COOLON AREA

EPM 5336 ‘Diamond Creek’, 30km south-south-west of Mount Coolon, was granted to Metana Minerals NL in April 1988. Several phases of reconnaissance rock chip and float sampling (81 samples) were carried out to explore for epithermal gold mineralisation in the Drummond Basin. This sampling returned Queensland Geological Record 2008/04 71 elevated to anomalous As, Sb and Sn from quartz diorites. Diorites at Boundary Hill are locally brecciated and silicified and a single anomalous rock chip assay result of 2.2ppm Au was obtained. Diorite breccias at Nobb Hill were generally of little interest, but a single sample from the southern flank of the hill assayed 1250ppm As and 160ppm Sb. A number of samples assayed as high as 550ppm Sb, 200ppm As and 85ppm Sn.

Two areas were soil sampled, but only low-order anomalies were outlined. Drill core from GSQ stratigraphic drill holes Mount Coolon 3 and 4 was sampled for geochemical and petrographic studies. Aerial magnetic and radiometric surveys were flown over part of the Diamond Creek area by Aerodata.

Five stream sediment samples were collected from the Boundary Hill area and processed for analysis for kimberlitic indicator minerals. Results were negative. The Permit was relinquished in February 1990.

CLERMONT AREA

EPM 5629 was granted to Burgundy Exploration Pty Ltd in November 1988. The company explored for gold mineralisation associated with the Ducabrook and Star of Hope Formations, 55km west of Clermont. Subsequent exploration focused on diamond and zeolite potential.

ACM Gold Ltd, in a joint venture, carried out stream sediment sampling and a gridded magnetic survey over previously defined aeromagnetic anomalies. Follow-up work included soil sampling and geological mapping. No intrusive or volcanic rocks were mapped within the tenement. The ground magnetic survey delineated Anomaly 4, west of Telarah Homestead, and Anomaly 3, adjacent to Pioneer Homestead. One hundred and twenty-two stream sediment samples were collected at a density of one per square kilometre and returned up to 2.69ppb Au. Follow-up and re-sampling returned up to 2.90ppb Au. However, rock chip samples of bedrock returned <0.007ppm Au. One hundred and four soil samples returned assay results of up to 3.24ppb Au. Soil samples from the sites of the aeromagnetic anomalies all returned very low gold contents. ACM Gold concluded that the mildly anomalous gold contents in stream sediments were derived from Cainozoic conglomerate and withdrew from the joint venture.

Burgundy Exploration, in association with Mount Gipps Ltd, carried out further exploration over a ground magnetic anomaly. Heavy mineral fractions were collected from soil samples. Laboratory tests indicated that the heavy mineral fractions consist of pyroxene, chromite, chrome diopside and limonite, with minor tourmaline, olivine, ilmenite and pyrope. The array of heavy minerals appeared to be indicative of kimberlites but the low magnesium content in the ilmenite and pyrope and low chrome content in diopside downgraded any kimberlite association.

Samples of zeolite were collected from an exposure of the Ducabrook Formation along the Clermont–Alpha Road, east of Telarah Homestead, and tested for 72 Cranfield & Diprose ammonia exchange capacity property. No significant results were obtained. The Permit was relinquished in July 1990.

EPM 5688 ‘Clydevale’ was granted to Austwhim Resources NL in January 1989. The Permit extended from north of Vanguard Creek to south of Eastern Creek, 75km west of Clermont.

An interpretation of airborne magnetic data delineated five target areas for exploration. Ground magnetic surveys were carried out over four of these anomalies. Twenty-two stream sediment samples were collected and examined for kimberlitic indicator minerals. Three out of thirteen mineral grains were identified as possibly being of kimberlite affinity. The anomalies and sources of the indicator minerals were considered likely to be basalt/gabbro plugs. The Permit was relinquished in December 1990.

ANAKIE AREA

EPMs 7547 ‘Zig Zag’ and 7548 ‘Bogantungan’ were granted to Cluff Resources Pacific Ltd in August 1990. The company planned to carry out grassroots exploration for diamonds in the Tomahawk Creek – Ironpot Creek area, west-north-west of Anakie. However, a revaluation of the costs involved in exploring the area resulted in a decision not to proceed with the exploration program. The Permits were relinquished in September 1991.

PROSTON AREA

EPM 13506 was granted to D Royle and South East Diamonds NL in February 2002. The target was diamonds in the Brigooda area.

An air photo interpretation was carried out in 2002. Ground magnetics were carried out over the area surrounding the Garnet Gully diamond occurrence. Soil samples were submitted for Mobile Metal Ion Leachant analysis to identify kimberlites. The samples were analysed for a specific set of minerals that have been previously identified as indicating a kimberlitic source. A heavy mineral concentrate sample was collected and analysed for kimberlitic indicator minerals and a selection of grains was forwarded for electron microprobe analysis. One grain was found to lie in the kimberlite compositional field and another four grains were very close. This suggested that diamond eclogite facies rocks are present at depth in this area and are the possible source of diamonds previously located in the area. An interpretation of Landsat imagery showed clusters of circular structures, some of which are associated with the magnetic anomaly.

Detailed geological mapping of the breccia pipe was carried out in 2003 and 90 soil samples were collected and processed for MMI geochemistry analysis. Granite is defined mainly by elevated Rb, Ti, Th, Sc, Y, U and Pb. Basalt is enriched in Mg, Ni, Cr, Co, Pd, Zr, Nd, Sc, Ce and La. Breccia could not be geochemically discriminated from basalt. It was speculated that ultrahigh pressure minerals such as garnet, sapphire and diamonds found associated with Tertiary Queensland Geological Record 2008/04 73 volcanics in eastern Australia can be brought to the surface by normal basaltic eruptions.

After reviewing all data collected over this area, it was decided that any diamond mineralisation would not be economically viable. The Permit was relinquished in February 2004.

EPMs 14284, 14285, 14287, 14289 to 14291 and 14339 were granted to Diamond Search Australia Pty Ltd in March and June 2004. These permits covered an area north-west and west of Kingaroy.

Geodiscovery Pty Ltd assessed the diamond potential of these permits for Diamond Search Australia. Available data, including geological and geophysical interpretations, were reviewed and a GIS-based project prepared. Numerous discrete magnetic anomalies with characteristics consistent with kimberlite or lamproite intrusions were identified. A stream gravel sampling program was proposed but nothing further was reported before the Permits were relinquished in March 2007.

EPMs 10048 and 10049 were granted to BHP Minerals Pty Ltd in April 1994. Breccia pipes in the Brigooda–Ballogie area were considered to be prospective for diamonds on the basis of their mantle-derived mineral content, associated undersaturated alkali basalts and the discovery of two macrodiamonds.

Nine samples were collected for diamond indicator mineral analysis and petrology. A ground magnetic survey was carried out on a one square kilometre grid over the southern pipe at Brigooda. The pipe did not display a distinct magnetic expression due to masking by the stronger signatures of basalts. A selection of heavy mineral grains was sent for microprobe analysis. The Brigooda samples contained high percentages of chrome diopside and other pyroxenes, with lesser amounts of mica, spinel, picroilmenite, ilmenite, garnet, iron hydroxides and amphibole. The Ballogie samples contained high percentages of iron hydroxides, spinel and pyroxene. K–Ar age dating returned dates of 19Ma for Brigooda and 43Ma for Ballogie.

Seven open hole, hammer and blade holes (222m) were drilled to test the pipes at Brigooda and Ballogie. The holes at Brigooda showed that the breccia is a 10m thick blanket overlying 7m of basalt on highly weathered granite. The breccia at Ballogie was 8m thick overlying weathered granite. The breccias are more likely to be volcanic ejectamenta than pipe structures. It is possible that there are pipes in the area that could have acted as vents for this material.

Two bulk samples were collected of 97t and 89t were collected from Brigooda and Ballogie, respectively, and processed for kimberlitic indicator mineral analysis. No diamonds were found. The Permits were relinquished in April 1996.

EPM 10192 was granted to Australian Kimberley Diamonds NL in August 1994. Interpretation of Landsat imagery was used to identify anomalous areas in the Brigooda area that might be of interest for diamond exploration. Five loam and 46 stream sediment samples were collected and analysed for kimberlitic indicator 74 Cranfield & Diprose minerals. Indicator minerals identified as being possibly kimberlitic were then sent for microprobe analysis. Six samples contained chromite grains that were possibly kimberlitic in origin. Two samples contained chromites that were considered to be close to the kimberlitic field. Four samples contained picroilmenite grains that, although not considered to be kimberlitic in origin, had a chemistry that was very close to kimberlite. Air photo interpretation of four sites that had returned kimberlitic type chromite identified anomalous circular structures. Follow-up sampling comprised 39 hand auger loam samples and 11 stream sediment samples. These samples underwent analysis for kimberlitic indicator minerals and one stream sediment sample was found to contain kimberlitic chromite. A technical review of the exploration data downgraded the potential for a diamond source being found in the area. The Permit was relinquished in August 1997.

PITTSWORTH AREA

EPMs 10084, 10311 and 10312 were granted to BHP Minerals Pty Ltd in May 1994 and October 1994.

An Airborne EM survey delineated a suite of conductors, most corresponding to topographic lows and some with coincident magnetic lows, in a basalt field at Pittsworth, 30km west of Toowoomba.. It was thought that they could be interpreted as mantle-tapping pipes. Twelve EM anomalies were identified for further testing Brief inspections were made of these anomalies. Most had no outcrop. An outcrop of breccia with abundant mantle xenoliths was observed in a road cutting at the edge of one anomaly. This breccia was intruded by a fresh basalt dyke with mantle xenoliths. A pyroclastic deposit of similar breccia also occurs at a quarry at Gowrie Mountain. Stream sediment samples were collected from eight sites. Petrographic examinations were made on samples of basalt and breccia. Ten samples were processed for kimberlitic indicator minerals and a selection of grains was sent for further analysis by electron microprobe. None of the minerals found was of kimberlitic origin.

Thirteen open hole blade and hammer holes (385m) were drilled to test twelve EM anomalies. Weathered basalt was intersected in all holes, either at the surface, or beneath a variable thickness of soil and of clay derived from basaltic saprolite. Fresh basalt was dark grey, fine-grained and non-porphyritic. No brecciation or xenoliths were observed in the drill samples.

It was concluded that the indicator minerals could be explained as being derived from basalts and that the EM anomalies correspond to the presence of clay. None of the volcanic breccias was shown to be derived from a pipe. The presence of mantle xenoliths indicates that there must be feeders in the vicinity. The Permits were relinquished in May 1996.

EPM 10263 was granted to Rudall Resources NL in November 1994. The Permit covered an area, 9km north of Pittsworth, that was considered prospective for diamonds. No field work was carried out in this area because the company Queensland Geological Record 2008/04 75 decided it would not be economically viable. The Permit was relinquished in January 1996.

STANTHORPE AREA

EPM 11420 was granted to Northern Territory Gold Mining NL in November 1996.

The company carried out a literature review, air photo interpretation and review of airborne magnetic and radiometric data. The target was diamonds in the area surrounding Stanthorpe, where diamonds have been recovered historically during tin mining operations. Twenty-one heavy mineral samples were collected and underwent analysis for kimberlitic indicator minerals. Four rock samples were also collected and were found to contain kimberlitic indicator minerals with similarities to those found in Pliocene sands. It was concluded that these minerals were not local in origin as there were indications that they had undergone extreme water transport and their source was probably outside of the Stanthorpe area. Therefore, the company would need to trace the source of Pliocene rivers to locate the source of the diamonds. The Permit was relinquished in November 1997.

CONCLUSIONS

Diamond exploration in Queensland has not led to the discovery of any economically viable deposits despite the recovery of diamonds in many parts of the state. The source of many of these diamonds has not been determined. Diamond exploration has generally followed the model that diamonds can only be found in kimberlite structures despite many other possible sources of diamonds, such as ultrabasic breccia pipes and as xenoliths in Cainozoic alkalic extrusives.

In many exploration programs, the number of samples collected has been relatively small. Exploration has been wound up despite recovering microdiamonds and indicator minerals. In many instances, companies concluded that the indicator minerals found were not of kimberlite origin but did no further testing on the samples.

Very little of the state has been comprehensively explored for diamonds and, even where exploration has occurred, it may have been flawed in either the sampling process or in the lack of importance given to the actual samples regardless of the contents. The Cainozoic alkalic volcanic provinces in the eastern part of the state form a large, relatively unexplored region in which at least one diamond has been found associated with diamond indicator minerals in south-east Queensland.

ACKNOWLEDGEMENTS

Some information in this report has been derived from an unpublished GSQ report authored by the late Dr Alan Robertson. His contribution to the sections on 76 Cranfield & Diprose diamond properties and the early exploration for diamonds in Queensland is acknowledged.

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