Pan Gem Resources (Aust) Pty Ltd 2011

Pan Gem Resources (Aust) Pty Ltd Gemstone Exploration Across Australia

Recent Advances to the Syntectonic Model and its Applicability to Opal Exploration along the Collarenebri Antiform

Dr. Simon R. Pecover Managing Director Pan Gem Resources (Aust) Pty Ltd

Abstract

Recent advances to the Syntectonic Model of opal deposit formation within the Great Australian Basin (GAB) have resulted from a detailed study of micro-structural features evident in opal veins within gently warped interbedded sandstones and claystones of the Angledool Antiform. This study has revealed opal vein textures that preserve repeated episodes of fluid flow injection by viscous Non Newtonian fluids, hyper-saturated with amorphous silica.

The preserved textures within these opal veins also show evidence of repeated episodes of opal hardening and brittle fracture deformation of earlier injected viscous fluids. These textures are interpreted to have been formed by multiple viscous opal fluid injection and hydraulic extension fracturing depositional events, resulting from opalising fluid flows under pressure, moving along progressively developing and evolving opal vein array systems.

Given the generally horizontal nature of the vein opal deposits studied, and their juxtaposition to facies change boundaries that have been subjected to faulting, generating relay-zone ―flats‖ and ―ramps‖ fault architectures, then these deposits could be classified as stratabound fault-controlled vein-type ore depositional systems.

From a regional perspective, the vein systems studied were found to mainly coincide with areas of high intensity faulting within very specific parts of mapped antiformal and domal structures, where compressional dewatering of silica-rich clay facies reservoir rocks appears to have provided highly localised sources of opalising fluid flows into nearby structural (i.e. both tectonic and sedimentary) trap sites and vein systems.

The Syntectonic structural opal formational analogue and paradigm provided by the opal depositional environment of the Angledool Antiform, has been applied to exploring the adjacent Collarenebri Antiform. Numerous structural targets have been identified along the Collarenebri Antiform, where high intensity faulting, suitable opalising fluid-source reservoir rocks and extensive silicification has been identified.

Introduction

Regolith genesis researchers have long advocated simple gravity-driven vertically-downward-moving meteoric groundwater flows, as the principal mechanism for carrying dissolved amorphous silica to depth across near-surface Great Australian Basin (GAB) sedimentary lithologies, with the resulting opal deposits said to have been formed by the evaporation of silica-rich waters, passively residing for millions of years in pre-existing open cavities. Additionally, some workers have even claimed a dominant role for microbes in the precipitation of opalising silica, co-genetic with the deposition of Cretaceous sediments across the GAB.

However, a new study of micro-structural geological features, preserved in opal veins formed after the deposition of the Cretaceous sediments of the GAB, has revealed a complex range of textures that preserve dynamic fluid flow and kinematic relationships that are interpreted to be indicative of multiple episodes of viscous Non-Newtonian opalising fluid flows at relatively high pore pressures. Complex patterns of intermixed potch and precious opal have been observed in some of the vein systems studied, which suggests once vigorous, dynamic and turbulent fluid flows through vein networks, flowing from areas of higher pore pressure to areas of lower pore pressure.

Pan Gem Resources (Aust) Pty Ltd 2011

Multiple episodes of opalising fluid injection, opal hardening and brittle fracture deformation, forming complex in-vein opal breccias, is considered indicative of multiple generations of opal formation, within a seismically active and vigorous fluid-flow-driven, hydraulic-extension-fracturing, Syntectonic environment.

The vein systems studied, were found to be located in areas of high intensity faulting and fracture- mesh development, within discrete lateral and vertical parts of the Angledool Antiform. The geological setting of these vein opal deposits within the Angledool Antiform has now provided a suitable analogue and paradigm for Pan Gem Resources and its joint venture partners, to progress opal exploration across the nearby Collarenebri Antiform, and is considered to have applicability across the entire opal prospective area of the GAB.

Core Tenants of the Syntectonic Model of Opal Formation in the Great Australian Basin

The ―Syntectonic Model‖ of Pecover (1996), advocates a core process in which the vein opal deposits of the GAB were formed rapidly through a process of fault controlled, seismic-fluid-pumping and hydraulic extension fracturing of host rocks, by silica-rich fluids derived from the compressional overpressuring and dewatering/silica-stripping of silica-laden claystones, during antiformal buckling of interbedded Cretaceous sandstones and claystones. The precipitation of opal from these silica- super-saturated fluids is thought to have occurred through the polymerisation of dissolved silica, which then formed viscous gelatinous silica/water mixtures hyper-supersaturated with colloidal silica spheres.

The potential contribution of fluids to the sedimentary pile of the GAB, from other sources, including hot artesian waters, is not excluded from the Syntectonic Model, and is supported by zirconium mobilisation research work carried out at Macquarie University (Liddicoat 2003).

At its core, the Syntectonic Model conforms to the well understood processes by which most mineral veins are thought to have been formed in nature. These processes typically involve hydraulic extension of fractures that become filled with mineralising fluids which move along pressure gradients within the structural architecture of the geologic system, with relatively rapid precipitation of minerals occurring within these fractures, during periods of depressurisation, leading to mineral vein formation. As processes of this type are commonly multi-cyclic, then it is not surprising that several generations of mineralisation can occur within a given vein system.

Thus, the core geologic and structural tenants of the ―Syntectonic Model‖ of opal genesis in the GAB (Figure 1), may be summarised as:-

 Kinematic  In-Veins  Stress Controlled  Syntectonic

Geotectonic Setting of Opal Deposits along the Angledool Antiform

Opal mined across the Angledool Antiform commonly occurs as potch and much rarer precious opal, in horizontal to sub-horizontal veins, interstitial infillings between mineral grains in some sedimentary lithologies, isolated nodules, ironstone concretion cavity infill’s, and as pseudomorphic replacements of fossil remains in generally clay-rich facies rocks.

At many widely-spaced locations along the Angledool Antiform, within the Narran-Warrambool Opal Mining Reserve (Figure 2), potch and precious opal occurs in highly faulted and fractured Cretaceous claystones and clayey sandstones. Fault and fracture-controlled deformation bands (known locally as

Pan Gem Resources (Aust) Pty Ltd 2011

―biscuit band‖) have also been found to be an important source of minable opal, at or close to the surface.

Within the Reserve, the opal-bearing Cretaceous sediments have been gently warped into low, generally NE-SW trending, ridges, forming low-amplitude antiformal and domal tectonic structures. In many areas, opal-bearing country is commonly overlain by hard caps of silicified Tertiary sands and gravels, which crop out as silcretes. In these extensively silicified areas, distinctive and discrete mounds of silcrete rubble, are interpreted by experienced prospectors, to be the surface expression of ―blows‖, and are considered valuable surface indications of opal prospective country (Aracic 1996).

It is well known by experienced opal miners’ across the GAB, that there is an absolute and intimate association between the location of faults and sites of opal deposition. Opal typically occurs close to the hanging wall and foot wall sides of these faults.

Faulting observed in open-cut and underground exposures across the Angledool Antiform, exhibits complex mixtures of fault types, including normal, reverse and oblique-slip faults, commonly arranged in conjugate sets, resembling wedge-like structures that severely disrupt the "level". Faults cross- cutting claystone "levels", may flatten appreciably, forming layer-parallel slip surfaces concordant to bedding, particularly at the contact between sandstone and claystone. These layer-parallel slip surfaces may be related to complex linkages within fault relay-zones, comprising horizontal fault ―flats‖ connected to nearby inclined fault ―ramps‖, forming discrete fault damage zones, in which dilational and hydraulic extension fractures within the ―flats‖ host opal vein arrays. Such vein arrays would be expected where slip surfaces show significant undulation, and a high degree of roughness. When multiple fault relay-zones are arranged en-echelon to one another in areas of intense fault clustering, opal veins may occur over considerable lateral distances, in a stepwise vein-array fashion.

In these sub-horizontal fault damage zones, complex layering and intermixing of bedding-parallel brecciation, fault gouge and networks of opal veins collectively define the ―opal horizon‖. These damage zones may also show significant horizontal to sub-horizontal slicken-sided surfaces, indicative of prolonged fault movement. In some areas, the opal horizon may also be developed at the base of a claystone unit immediately overlying a sandstone unit. This development of "top" and "bottom" opal-bearing horizons may also be accompanied by the stacked succession of several opal levels, each hosting opal mineralization at repetitive sandstone/claystone interfaces.

The fault and bedding-controlled vein systems within the Angledool Antiform, commonly exhibit complex meshwork patterns of branching and anatomising veinlets, similar to those seen in fault- controlled net-vein fracturing geological environments. The opal veins typically show pinch and swell morphologies when viewed in cross-section. Lateral extent, like thickness, is highly variable and ranges from small centimetre-scale pods to undulating vein arrays that can be traced over tens of metres.

In all the opal fields occurring across the Angledool Antiform, extensive vertical fracturing of both sandstones and claystones is evident. These vertical fracture sets resemble Hill-Type fracture meshes, commonly developed in many parts of the world, where fluid flow, induced by seismic-fluid pumping processes, has occurred in horizontally bedded sandstones and shales (Sibson 1987, 1989 & 1994).

Across the Angledool Antiform, these fracture meshes may be associated with normal and reverse faults, which may also host brecciated stockworks and vertical pipe-like ―chimneys‖ of brecciation (known locally as ―blows‖). These conduits provide evidence that fluids have travelled vertically upwards under pressure through the sedimentary pile. This process has given rise to a variety of geological structures, ranging from simple net vein fracturing of host rock lithologies, to angular clast- supported jig-saw-fit breccias, to matrix-supported breccias with rounded clasts; with the latter resulting from the prolonged fluidisation of the breccia column. While not all such breccia bodies have

Pan Gem Resources (Aust) Pty Ltd 2011 provided conduits for opalising fluids (as clearly, many breccias in GAB rocks are not silicified), those that are indurated and hardened by significant amounts of amorphous silica, are more likely (in the authors view) to be associated with areas of significant opal vein mineralization (Pecover 1996, 1999, 2003, 2005, 2007 & 2010).

The close association of those breccia pipes that display intense opal silicification and kaolinisation with nearby opal vein arrays, suggests an important genetic link between breccia formation, fault and fracture development, and significant lateral and vertically-ascending, opalising fluid flows.

Thus, given the generally horizontal nature of the vein opal deposits studied, and their juxtaposition to facies change boundaries, that have been subjected to faulting that has generated significant ―flats‖ and ―ramps‖ relay-zones, then the opal deposits within the ―flats‖ could be classified as stratabound fault-controlled vein-type ore depositional systems (Pecover 2010).

Recent Advances to the Syntectonic Model through the Study of Opal Vein Textures

To investigate the processes of opal vein formation in the GAB at the micro-scale level, samples of opal veins comprising multiple generations of potch, as well as mixtures of potch and precious opal, have been studied in detail.

This research has revealed a range of textures and features that demonstrate the dynamic processes by which opalising fluids have deposited multiple generations of potch and precious opal into evolving vein systems. This investigation also provides the basis for new lines of research into how viscous opalising fluids have behaved to produce the myriad of opal patterns and textures encountered in opal mines all across the GAB.

This research also supports the proposition, that the opal deposits of the GAB were primarily formed during the Tertiary Period, by tectonically-driven near-surface fluid flow processes associated with the antiformal warping, faulting and fracturing of water-saturated overpressured silica-rich clayey reservoir rocks, within the upper sedimentary sequence of Cretaceous rocks making-up the GAB, as advocated by the ―Syntectonic Model‖ of Pecover (1996).

Pan Gem Resources Opal Vein Research in the GAB

The following discusses the opal vein textural features identified during current opal genesis research carried out by the Author, with the financial support of Pan Gem Resources (Aust) Pty Ltd.

Potch Opal Vein Textures

The opal vein textures studied, record histories of incremental and multiple episodes of opal deposition via the injection of viscous opalising fluids. Earlier formed generations of opal in the veins studied show evidence of hardening and subsequent brittle fracture deformation. Parallel and cross- cutting relationships to previously formed veins were also found to be common, while fragments, slivers and blocks of rotated wall rock clasts, incorporated into the composite structure of the veins, resulted in complex wall rock and opal vein brecciation textures (Figure 3).

Complex patterns of cross-cutting, and vein-wall-parallel brittle-fracture micro-faulting, was also found to be common in the veins studied. Small-scale dyke-like intrusions of opal, comprising fluidised mixtures of both viscous and previously hardened opal clasts were found to occur along fractures in previously hardened opal (Figure 4). Some of these micro intrusions show evidence of dissolution and erosion/corrosion along the walls of the dykes, suggesting a vigorous and chemically corrosive siliceous fluid flow environment, even at the micro level.

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Clear textural evidence for the viscous nature and Non Newtonian fluid flow behaviour of the opalising fluids that formed the veins examined, can be seen where injecting fluids (now frozen) display distinctive curved fluid-flow-front patterns of movement, resulting from fluid drag along vein and internally intrusive micro-dyke walls (Figures 3, 4 & 5). Compelling textural evidence for turbulent viscous fluid flow of once liquid opal, which has become hardened and then fractured in a brittle manner through hydraulic extension fracturing, leading to new opal vein formation, can be seen in Figure 6.

Composite Potch and Precious Opal Vein Textures

Evidence of complex and dynamic processes in the formation of opal in GAB rocks, can be seen in opal veins displaying vein-wall-parallel stratification of both potch and precious opal. Particularly intriguing are those veins that show ―colour bars‖ sandwiched between layers of potch (Figures 7 & 8).

In some of the veins studied, the colour bars were found to be composed of precious opal comprising distinctive close-packed fibrous crystalline structures (Pecover 1996), consistent with the formation of colloidal photonic crystals (Colvin 2001). These crystals were found to have grown as closely- packed, sub-parallel crystal aggregates, with individual crystals displaying extreme length to width ratios, and orientated at right angles to vein stratification (Figure 7). In contrast, the potch layers in these veins, on either side of the ―colour bars‖, showed both laminar and turbulent viscous fluid flow textures.

In many of the stratified potch/precious opal veins examined, bands of potch and precious opal display simple to very complex interlayer laminar and turbulent viscous fluid flow relationships, involving the fluid mixing, diffusion and intrusion of multiple generations of potch and precious opal.

In these types of veins, the distinctive, undisturbed close-packed parallel aggregates of photonic colloidal crystals of precious opal, orientated normal to vein walls, is lacking, with laminar and turbulent fluid flows having generated a flowing "crystal mush" of broken and re-distributed photonic colloidal crystals, creating intriguing patterns of liquid-crystal-fire (Figure 8).

Why Precious Opal is so Rare in GAB Rocks

As the growth of photonic colloidal crystals of precious opal, presumably requires relatively stable and quiescent conditions to form (e.g. Figure 7, Specimen A.), then the textures evident in specimens B, C & D of Figure 7, indicate that these conditions can be severely disrupted by later invading fluid flows of viscous liquid potch opal. Furthermore, the laminar and turbulent liquid-opal- fluid-flow conditions affecting silica gels containing disordered accumulations of generally non- equidimensional sized silica spheres, within dynamically evolving Syntectonic opal vein arrays, would tend to work against the orderly arrangement of close-packed silica spheres to form photonic colloidal crystals, and accordingly, the creation of effective light diffraction gratings; so necessary for the formation of precious opal.

Thus, in a dynamically forming and evolving Syntectonic opal vein depositional system, channelized flowing "rivers" of viscous siliceous fluids, carrying a jumbled mass of silica spheres, from areas of high pore pressure to areas of low pore pressure, in response to fault-controlled seismic fluid pumping processes, would greatly favour the formation of potch opal over precious opal (i.e. because the silica spheres in such a dynamic fluid-flow environment would have virtually no opportunity to arrange themselves into orderly close-packed light-diffracting arrays).

In contrast, precious opal would likely only form in those "quiet" parts of the opal depositional system (e.g. within sealed fluid-filled compartments), that allowed for the stable and orderly assembladge of

Pan Gem Resources (Aust) Pty Ltd 2011 close-packed equidimensional-sized silica spheres, and the subsequent growth of photonic colloidal crystals.

Therefore, in such a dynamic liquid-opal-fluid-flow geological environment, the formation of precious opal would be rare and the formation of potch opal would be very common.

Opal Vein Formation

The textural features described above, together with the inclusion of comminuted wall rock clasts within the veins examined, strongly suggests a tectonically-driven multi-cyclic process of opal vein formation in the GAB. Such a process would likely involve cyclic fracture-induced permeability, coupled with multiple fluid injection events associated with elevated pore pressures.

The Non Newtonian fluid flow textures preserved in the veins studied, also show the apparent mixing of different types of viscous fluids, with some veins preserving liquid flow patterns of precious opal intermixed with various types of potch opal. These features also suggest a cyclic formational process, involving episodically induced fracture permeability coupled with self-sealing along dynamically evolving fluid migration pathways (i.e. the vein arrays), and are thus unlikely to be the result of weathering and microbial formational processes.

Given that precious opal is likely to require quiescent conditions to achieve orderly packing of silica spheres to form a light diffracting array, then the stratification described above and the turbulent intermixing of potch and precious opal in the veins examined, points to a far more complex and dynamic fluid flow environment of opal deposition than has previously been contemplated by those advocating simple passive weathering and microbe geo-formational process models.

The opal vein textures described above, clearly show that passive rock weathering processes and the activity of so-called microbes (assuming of course that such filamentous structures reported from Australian opal, are indeed the fossil remains of real microbes, and not simply colloidal ligands and microbe-like silica nanoparticles, associated with colloidal chemistry processes) could not have formed the opal veins studied, and that complex textures preserving both viscous fluid flow and brittle fracture deformation are more likely to have been formed by fluids under pressure, associated with tectonic processes during opal vein formation, that were imposed on the near-surface Cretaceous sedimentary rocks of the GAB, after they were laid down.

Pan Gem Resources Opal Vein Formation Research Applicable to Exploration along the Collarenebri Antiform

The knowledge gained from the study of opal vein textures described above, has been used by Pan Gem Resources to better predict the depositional environments for opal deposition within GAB antiformal structures. Those areas which display stratigraphic and structural geometries favouring the formation of trap sites for opalising fluid accumulation, particularly within the ―flats‖ component of fault relay-zones, are considered by the author to be high priority opal exploration targets.

A number of such prospective sites associated with high concentrations of faults and surficial deposits of silcrete have now been identified during opal exploration along the Collarenebri Antiform. These sites also show many of the surface indications described by Aracic (1996) that are associated with known opal deposits across the Angledool Antiform.

Structural Setting of the Collarenebri Antiform

Structurally, the Cretaceous sediments of the Collarenebri Antiform (Figure 9) are part of the Byrock Lightning Ridge Composite Block (Figures 10 & 11). This structural block is bounded by large

Pan Gem Resources (Aust) Pty Ltd 2011 regional scale lineaments, which separate the block from the Boomi Trough in the east, the Coonamble Embayment in the south, and the Cunnamulla Shelf to the west. The block also coincides with the southerly extension of the Dirranbandi Syncline (Exon and Den Hertog 1972). The Cretaceous ridge country at Collarenebri is bounded by two very large continental-scale ENE - WSW trending lineament fracture systems. These are the Darling River Lineament to the west, which controls the drainage of the Darling River to the south-west and the Culgoa River to the north-east, and the Cobar-Inglewood Lineament, which controls the drainage of the Barwon River from Walgett, north-east to where it joins the Macintyre River, west of Goondiwindi. The Darling River Lineament and the Cobar-Inglewood Lineament are also broadly conformable to a pervasive ENE-WSW structural trend that is evident across most of NSW (Scheibner 1973 and 1979).

At Collarenebri, the regional structural setting is dominated by the Weemelah Block and the Cobar- Inglewood Kink Zone, with much of the area covered by opal Exploration Licences 6738 and 7650, occurring between the south-eastern edge of the Cobar-Inglewood Kink Zone, and the north-western edge of the Weemelah Block (Figures 10 & 11).

Opal prospective WNW-ESE-trending structures, comprising joints and fractures lie within ENE-WSW- trending structural corridors across outcropping Cretaceous sediments of the Collarenebri Antiform. As at Lightning Ridge, these structures appear to be prospective for the location of opal fields. However, the aeromagnetic mapping over the Collarenebri Antiform does not support the existence of a so-called ―Opal Corridor‖, such as the one proposed for the Angledool Antiform (which curiously does not seem to include the opal fields of Lightning Ridge proper).

Opal Exploration Targets Across the Collarenebri Antiform

Geological interpretation of Landsat and aerial photo imagery, coupled with ground-based geological mapping, has identified a large number of highly prospective structural and litho-stratigraphic targets for more detailed opal exploration across the Collarenebri Antiform. In particular, faults and fractures, striking at 0o to 10o, 30o to 45o, 60o to 90o and 325o to 355o respectively across the Collarenebri Antiform are considered highly prospective structural targets for opal mineralisation (Figure 12). Within this structural architecture, current exploration has located a number of areas of intense fault clustering associated with zones of brecciation, and argillic/silicic alteration of Cretaceous sediments, which are considered prospective for opal mineralisation at depth (Figure 13).

The most interesting of the prospective areas identified to-date, is Opal Prospect A, located in the northern part of the Collarenebri Antiform, where both potch and precious opal have been identified from drill hole samples. The prospect contains a number of brecciated silcrete outcrops associated with areas of significant argillic alteration located within a fault-cluster-complex that includes both normal and reverse faults. Prospective claystone reservoir rocks overlain by sandstone beds occur within the prospect area; with the stratigraphy displaying Hill-Type fracture sets containing vertical zones of brecciation and pervasive silicification (Figure 14).

Future exploration will concentrate on better defining the structural and stratigraphic architecture of the prospective areas identified along the Collarenebri Antiform, as well as characterising the mineralogy of the opal depositional system, and in particular, the nature and distribution of opal- bearing dilatational jogs and vein systems within fault relay-zone ramp and flat structural settings.

Concluding Remarks

During the last 15 years, since the Syntectonic Model of opal formation in the GAB was first proposed (Pecover 1996), considerable complimentary evidence has been presented by a number of researchers (Glass - van der Beek 2003; Liddicoat 2003, Verberne 2004; Rey, Verberne and Glass- van der Beck 2005; Rey & Dutkiewicz 2010).

Pan Gem Resources (Aust) Pty Ltd 2011

Much of this evidence is consistent with the fault-valve tectonic processes of mineralising fluid flow formation, proposed by Sibson (1987, 1989, 1990, 1994, 1996 & 2000), associated with fault-fracture mesh development, and the seismic pumping of geo-fluids in ore deposit settings across the planet. Importantly, such processes are known to be applicable to the formation of fault-controlled vein-type ore deposits in a variety of geological settings (Micklethwaite and Cox 2004).

However, many ―old-school‖ proponents of traditional weathering and biological processes still advocate opal forming mechanisms which do not adequately explain the formation of opal veins in the GAB.

As the head of a successful, privately funded, gemstone exploration and mining company, that has been in business for over 15 years, I for one would not invest in opal exploration and resource development projects, based on the formational mechanisms advocated by both the deep weathering and microbe models of opal deposit genesis in the GAB.

From a practical gemstone explorationist perspective, I believe that geo-formational models that provide little predictive value for targeting drill holes to discover new opal deposits are of no commercial value to the Opal Industry going forward.

Rather (and in deference to the on-going debate), in the absence of the application of any particularly agreed geological model to aid in the search for opal deposits across the GAB, newcomers need only to initially acquaint themselves with the published works of long-time opal miner, Mr. Stephen Aracic (1996), to understand and appreciate the most important and practical indications to observe when exploring for and mining opal deposits throughout the Great Australian Basin.

Bibliography

Aracic, S., 1996. DISCOVER OPALS, LIMITED EDITION. BEFORE & BEYOND 2000, WITH SURFACE INDICATIONS, p 352. Stephen Aracic, Lightning Ridge NSW.

Bourke, D.J., 1973. A geological interpretation of the composite log of the Lightning Ridge town water supply bore. New South Wales Geological Survey ——— Report GS 1973/027 (unpubl.).

Colvin, V.L., 2001. From opals to optics: Colloidal photonic crystals. Materials Research Society Bulletin, 26 (8), 637-64.

Cram, L., 1990. BEAUTIFUL AUSTRALIAN OPALS, p 24. Len Cram, Lightning Ridge NSW.

Cram, L., 1998. A Journey with Colour. A History of Queensland Opal, pp 1- 368. Len Cram, Lightning Ridge NSW.

Exon, N.F., and Den Hertog, J.G.A., 1972. Geology of the Northern Part of the Surat Basin. Sheet A, 1:1,000,000. Australian Bureau of Mineral Resources, Canberra.

Glass - van der Beek, I., 2003. Structural and lithological relationships to opal deposition at Lightning Ridge, NSW. B.Sc. (Hons) thesis, University of Sydney, Sydney, 92 pp.

Hawke, J.M., and Bourke, D.J.., 1984. Stratigraphy, in Contributions to the geology of the Great Australian Basin in New South Wales. New South Wales Geological Survey ——— Bulletin 31, 23-124.

Hawke, J.M., and Cramsie, J.N., 1984. Structural Subdivision of the Great Australian Basin in New South Wales, in Contributions to the geology of the Great Australian Basin in New South Wales. New South Wales Geological Survey ——— Bulletin 31, 1-22.

Pan Gem Resources (Aust) Pty Ltd 2011

Henricus Prematilleke 2007. Australia Gemstone Report. Jewellery News Asia Magazine, pp45-62, January 2007. Published by CMP Asia Ltd, Hong Kong.

Holmes, G.G., and Senior, B.R., 1976. Lightning Ridge Opal Field. International Geological Congress, 25th, Sydney ——— Excursion Guide 7B. 13pp.

Liddicoat, K.M., 2003. Geology and geochemistry of the Lightning Ridge black opal deposits. B.Sc. (Hons) thesis, Macquarie University, Sydney, 166 pp.

Micklethwaite, S., and Cox, S.F., 2004. Fault-segment rupture, aftershock-zone fluid flow and mineralisation. Geological Society of America, Geology; v. 32; no. 9; p. 813–816.

Oliver, J.G and Townsend I.J., 1993. Gemstones in Australia. A review of the industry and the first national assessment of gemstone resources. Australian Gemstone Industry Council pp.1-72. Australian Government Publishing Service, Canberra.

Paradis, S. Townsend, J. and Simandl, G.J. (1999): Sedimentary-hosted Opal; in Geological Fieldwork 1998, B.C. Ministry of Energy and Mines, Paper 1999-1.

Pecover, S.R., 1996. A new genetic model for the origin of opal in the Great Australian Basin. Mesozoic Geology of the Eastern Australian Plate Conference. Geological Society of Australia, Extended Abstracts 43, pp 450-454.

Pecover, S.R., 1999. The new syntectonic model of origin to explain the formation of opal veins (―seams‖ and ―nobbies‖), breccia pipes (―blows‖) and faults (―slides‖) at Lightning Ridge. 1st National Opal Symposium, Lightning Ridge, Extended Abstracts, pp 1-8.

Pecover, S.R., 2003. Structures related to opal deposits at Lightning Ridge. Opal Exploration Symposium, Earth Resources Foundation, The University of Sydney, Extended Abstracts, pp 1- 5.

Pecover, S.R., 2005. Breccia Pipes – Fluid pathways of the opal gods. 4th National Opal Symposium, Lightning Ridge, Extended Abstracts, pp 1-31.

Pecover, S.R., 2007. Australian Opal Resources, Outback Spectral Fire. Rocks and Minerals, 82(2) 102-115.

Pecover, S.R., 2010. Fluid flow and brittle fracture textures in opal veins: Clues to the origin of opal in the Great Australian Basin. 13th Quadrennial IAGOD Symposium, Adelaide, Extended Abstracts, pp 420.

Redfire Resources N.L., 1992. Prospectus to raise $AUD 2.5 million for the development of opal resources in NSW and Queensland.

Redfire Resources NL., 1991. Exploration Reports, ELs 3573 & 3574, Collarenebri, Lightning Ridge area. First annual exploration report, period ending Jul 1991. Unpublished report. GS1991/235 (R00000700).

Redfire Resources NL., 1992. Exploration Reports, ELs 3573 & 3574, Collarenebri, Lightning Ridge area. Second annual exploration report, period ending Jul 1992. Unpublished report. GS1991/235 (R00000701).

Redfire Resources NL., 1993. Exploration reports, ELs 3573 & 3574, Collarenebri, Lightning Ridge area. Third annual explor. report, period ending July 93. Unpublished report GS1993/228 (R00003130).

Pan Gem Resources (Aust) Pty Ltd 2011

Redfire Resources NL. 1994. Final report, ELs 3573 & 3574, Collarenebri, Lightning Ridge area. Fifth annual & final explor. report, period ending Nov 93. Unpublished report .GS1994/169 (R00000317).

Rey, P.F., Verberne, R.T., and Glass-van der Beck, I., 2005. Some remarks about the formation of Boulder opal. 4th National Opal Symposium, Lightning Ridge, Extended Abstracts, p 4.

Rey, P.F., and Dutkiewicz, A., 2010. The formation of seam opals at Lightning Ridge. 13th Quadrennial IAGOD Symposium, Adelaide, Extended Abstracts, p 424-425.

Scheibner, E., 1973. Tectonic Map of New South Wales, scale 1:1,000,000. Geological Survey of NSW, Sydney.

Scheibner, E., 1974. Fossil fracture zones, segmentation and correlation problems in the Tasman Fold Belt system. Reprint from The Tasman Geosyncline Symposium, Geological Society of Australia, Queensland Division, Brisbane.

Scheibner, E., 1979. Geological significance of some lineaments in New South Wales. The First Australian Landsat Conference - Proceedings LANDSAT 79, 318-332.

Sibson, R.H., 1987. Earthquake rupturing as a mineralizing agent in hydrothermal systems. Geology, Vol 15, pp 701-704.

Sibson, R.H., 1989. Structure and mechanics of fault zones in relation to fault-hosted mineralization. AMF Special Publication, p 66.

Sibson, R. H. 1990. Conditions for fault-valve behaviour. In: Deformation Mechanisms, Rheology and Tectonics (edited by Knipe. R. J. & Rutter, E. H.). Spec. Publ. geol. Sot. Lond. 54, 15-28.

Sibson, R.H., 1994. Crustal stress, faulting and fluid flow. In Geofluids: Origin, Migration and Evolution of Fluids in Sedimentary Basins, Ed Parnell, J., Geological Society Special Publication No 78, pp 69- 84.

Sibson, R. H. 1996. Structural permeability of fluid-driven fault-fracture meshes. Journal of Structural Geology, Vol. 18, No. 8, pp. 1031 to 1042.

Sibson, R.H., 2000. Tectonic controls on maximum sustainable overpressure: ﬂuid redistribution from stress transitions. Journal of Geochemical Exploration 69–70 (2000) 471–475.

Townsend I.J., 2007. Perfect conditions, perfect spheres: Opal formation in Australia In Opal The Phenomenal Gemstone, pp18-21. Publisher, Lithographic, LLC, East Hampton, Connecticut, USA, 1-112.

Verberne, R.T., 2004. Formation of opal deposits at Lightning Ridge, New South Wales, Australia. A descriptive study into the mode of opal deposition. Utrecht University, the Netherlands and The University of Sydney. Post doctoral study pp 1-23 (unpubl).

Watkins, J.J., 1985. Future prospects for opal mining in the Lightning Ridge Region. New South Wales Geological Survey Report GS 1985/119.

om ved fr s deri cks, fluid oir ro lising eserv nes Opa ured r laysto press sed c over mpres as co such 04 Cox 20 aite & klethw ter Mic ified Af m Mod Diagra

Figure 1. Geological characteristics consistent with the Syntectonic Model of opal formation in the Great Australian Basin.

Dr. Simon R. Pecover, 2011 Figure 2. Angledool Antiform, within the Narran-Warrambool Opal Mining Reserve. Modified after NSW Mineral Resources opal fields Landsat imagery. Micro faults, fractures and opal veins cross-cutting earlier A formed potch layers

Dr. S. R. Pecover Specimen & Photo Layer-parallel fractures in-filled by later a generation of potch

Anastomosing fracture in-filled by a possible 4th generation of potch Micro potch breccias

Multiple generations of potch Potch vein containing showing viscous fluid flow textures fragments of earlier-formed opal B Dr. S. R. Pecover Specimen & Photo Sandy claystone clasts ripped from vein walls Brecciated wall and carried along in rock clasts a viscous liquid opal fluid flow Curved viscous opal fluid-flow-fronts

Mixing of potch and precious opal viscous fluids

Sandy claystone wall rock host to opal veins

Fluid mixing Opal veinlet front showing sense of hydraulic extension Curved viscous precious opal fluid-flow-fronts Fluid mixing front Figure 3. A. Horizontally laminated vein of potch opal, cross-cut by multiple fractures that have been in-filled by later generations of opal, all showing viscous fluid flow and brittle fracture deformation textures. B. Complex vein of intermixed potch and precious opal, showing curved viscous fluid flow fronts around brittle-fractured wall rock clasts.

Dr. Simon R. Pecover, 2011 Curved viscous fluid flow-fronts A of once liquid opal

Laminar viscous fluid flow

Dr. S. R. Pecover Specimen & Photo

Intrusive opal dyke

Patterns of Fluid mixing Intrusive turbulent viscous fronts opal fluid-flow dyke Brecciated opal

Sandy claystone wall rock Wall rock brecciation

B Curved viscous fluid-flow-fronts of once liquid opal

Dr. S. R. Pecover Specimen & Photo

Intrusive opal dyke

Laminar viscous Laminar viscous fluid-flow fluid-flow Figure 4. A. & B. Composite veins of potch showing numerous complex relationships between multiple generations of opal, showing a variety of viscous fluid-flow behaviors. Dyke-like intrusions are clearly evident in both specimens, as are well developed curved viscous fluid-flow-fronts of once liquid opal. Rheological differences between opal generations, ranging from plastic to brittle fracture deformation, are also clearly evident in these veins. Dr. Simon R. Pecover, 2011 Brittle-fractured Curved viscous fluid-flow-fronts clasts of potch Dr. S. R. Pecover Specimen & Photo A of once liquid opal

Patterns of turbulent viscous fluid-flow within laminar flow Large clast of earlier-formed potch showing laminar & turbulent viscous fluid-flow patterns

Sandy claystone wall rock Brecciated opal & sandy claystone wall rock clasts B Rotated potch clast

Patterns of Fluid mixing turbulent viscous fronts fluid-flow

En echelon micro reverse En echelon micro faults with intrusive Fractured opal veins reverse faults potch dykes & sandy claystone wall rock Fractured opal veins & sandy claystone wall rock

Micro normal fault Dr. S. R. Pecover Specimen & Photo

Figure 5. A. & B. Composite veins of potch showing numerous complex relationships between multiple generations of opal, showing a variety of viscous fluid-flow behaviors. Dyke-like intrusions are clearly evident in both specimens, as are well developed curved viscous fluid-flow-fronts of once liquid opal. Rheological differences between opal generations, ranging from plastic to brittle fracture deformation, are also clearly evident in these veins.

Dr. Simon R. Pecover, 2011 Turbulent viscous fluid-flow of liquid potch opal

Laminar viscous fluid-flow of liquid potch opal

Hydraulic extension fractures in-filled with a later generation of viscous liquid potch opal, forming a younger opal vein within an older opal vein Dr. S. R. Pecover Specimen & Photo

Figure 6. Turbulent and laminar viscous fluid-flow of potch opal, cross-cut by hydraulic extension fractures in-filled by a later generation of potch opal. The turbulent fluid flow patterns evident in this specimen, record classic Non Newtonian viscous flow behavior. While ever these processes are at work within a developing and evolving Syntectonic opal vein depositional system, precious opal is prevented from forming (which is why precious opal is so rare). Dr. Simon R. Pecover, 2011 A Photonic colloidal B Potch crystals of precious opal

Potch Potch

Potch

Potch Potch

Len Cram Photo

Corrosion & disaggregation of precious opal layer by C potch opal fluid flow D Potch

Laminar & wavy viscous fluid flowing potch opal

Photonic colloidal crystals of precious opal breaking-up in laminar & viscous fluid flowing potch opal Figure 7. A. Colour bar within translucent potch, comprising parallel photonic colloidal crystals of precious opal that have grown at right angles to the prevailing opalising fluid lamination. B. Colour bars of precious opal within wavy viscous fluid flow layers of potch. C. Colour bars of precious opal being invaded, corroded and disaggregated by viscous fluid flow layers of potch. D. Photonic colloidal crystals of precious opal breaking apart and moving within laminar and wavy viscous fluid flows of potch opal. As the growth of photonic colloidal crystals of precious opal presumably requires relatively stable and quiescent conditions to form, then the textures evident in samples B, C & D suggest that these conditions can be disrupted by later invading fluid flows of viscous liquid opal. Furthermore, the laminar and turbulent conditions of liquid opal fluid flow within dynamically evolving Syntectonic opal veins would tend to prevent the orderly close-packing of silica spheres and the creation of light diffraction gratings. Thus, in a dynamically forming and evolving Syntectonic opal vein depositional system, containing flowing "rivers" of viscous liquid opal, moving from areas of high pore pressure to areas of low pore pressure, in response to fault-controlled seismic fluid pumping processes, potch opal formation would be greatly favoured over the formation of precious opal, with precious opal only being able to form in those "quiet" parts of the opal depositional system that allowed for the stable and orderly assembly of close-packed equidimensional sized silica spheres, and the subsequent progressive growth of photonic colloidal crystals.

Therefore, in such a geological environment, the formation of precious opal would be rare and the formation of potch opal would be very common. Dr. Simon R. Pecover, 2011 Laminar to turbulent Laminar to turbulent viscous fluid flows viscous fluid flows of potch opal, of precious opal, intruding comprising B A "crystal mush" broken of precious fragments opal of photonic Precious opal Precious opal colloidal "crystal mush" "crystal mush" crystals

Fluid flow patterns in potch opal Precious opal "crystal mush"

Fluid-flow-fronts Precious opal between potch Fluid flow patterns "crystal mush" in potch opal and Len Cram Photo precious opal

Curved viscous fluid-flow-fronts C of once liquid precious opal D Fluid-flow direction

Fluid-flow-fronts between potch and precious opal

Horizontal layers of potch and precious opal. Figure 8. A.-D. Laminar and turbulent viscous fluid-flow patterns of multiple generations of potch and precious opal.

In all of the above samples, complex patterns of intrusion and mixing of different generations of viscous liquid potch and precious opal are evident. Distinctive, undisturbed close-packed parallel clusters of photonic colloidal crystals of precious opal, orientated normal to vein walls, are lacking in these specimens, with laminar and turbulent fluid flows having generated flowing "crystal mushes" of broken and re-distributed photonic colloidal crystals, creating intriguing patterns of liquid-crystal-fire.

Dr. Simon R. Pecover, 2011 Figure 9. Landsat image of the Collarenebri Antiform covered by opal Exploration Licence 6738.

Dr. Simon R. Pecover, 2011 Figure 10. Structural settings of the Angledool and Collarenebri Antiforms.

Figure 11. Structural and magnetic settings of the Angledool and Collarenebri Antiforms. Dr. Simon R. Pecover, 2011 Figure 12. Structural architecture of the Collarenebri Antiform, showing major interpreted lineaments and faults.

Dr. Simon R. Pecover, 2011 Figure 13. Opal exploration targets across the Collarenebri Antiform, located in areas of high intensity faulting (Note: Many more targets have been identified than just the ones shown here).

Dr. Simon R. Pecover, 2011 Figure 14. Stratigraphy of Opal Prospect A, showing vertical Hill-Type fractures containing breccia pipes in the NE sector of the prospect. A high degree of silicification and argillic alteration of the fault damage zones are evident in this sector, which are overlain by thick deposits of surficial silcrete. Both potch and precious opal have been recorded from this Prospect.

Dr. Simon R. Pecover, 2011