Issue 52 May 1996

crustal scale feature, the Peace River- Prairie-Type Sedimentary Au-Ag-Cu Mineralization Athabasca Arch (Fig. 1), has periodically been reactivated producing a number of north- Hugh J. Abercrombie, GSC, Calgary Group is overlain by limestones, shaly lime- easterly trending normal faults and horst/gra- stones, shales, and minor evaporites of the ben structures of limited vertical extent. Karst Introduction Late Devonian Beaverhill Lake Formation. development at the pre-Cretaceous unconfor- Although the Western Canada Sedimen- Together, the Devonian rocks make up part of mity and at the contemporary land surface tary Basin (WCSB; Fig. 1) is better known as a Paleozoic through early Mesozoic passive further complicates structural relations. Tex- an energy basin, it is also well known for margin sequence which now is unconfor- tures indicative of elevated temperatures, world class sedimentary-hosted Zn-Pb depos- mably overlain by siliciclastic sediments of such as replacive sparry dolomite known at its at Pine Point, NWT. As a test of the hy- the mid-Mesozoic-Tertiary Rocky Mountain Pine Point and elsewhere in the basin, are ab- pothesis that other potentially economic con- foreland basin. At Fort MacKay, continental sent. Apatite fission track and organic matu- centrations of metals and other elements to peritidal sandstones of the Early Cretaceous ration studies indicate that maximum burial might be associated with evaporite-associated McMurray Formation host the Athabasca tar temperatures at the surface of the Precambrian brines in the WCSB, the GSC undertook a sand deposit which presently accounts for ap- did not exceed 90°C in the Fort MacKay area. program to investigate trace element enrich- proximately 21 % of Canada’s oil production. Mineralogy ment in brines and brine-associated rocks of Structurally the area is relatively simple. Methods the WCSB. This work led to the discovery of Salt dissolution within the Prairie Formation Au-Ag-Cu and related mineralization in sedi- (Elk Point Group) has caused localized fault- The mineralogy of core and outcrop sam- mentary rocks of the WCSB and the underly- ing, collapse and brecciation of overlying ples of basement granitoids, Devonian red ing Precambrian basement in the vicinity of strata along a northwesterly trending zone beds and carbonates, and Cretaceous sand- Fort MacKay, northeastern Alberta (Fig. 1; paralleling the eastern margin of the WCSB. stones has been determined using high reso- Abercrombie and Feng, 1994; Feng and Ab- Additionally, a major northeasterly-trending lution scanning electron microscope (SEM) ercrombie, 1994). Prairie-type mineralization consists of disseminated micro Au, Ag, Cu, with native, GSLSZ intergrown, and alloyed metals, and metal- chloride, -sulphide, -carbonate, and -oxide TA PP minerals deposited in pores and micro-vein- lets associated with fractures and diageneti- cally altered fabrics in sedimentary and crys- talline rocks of the WCSB. It has been observed from basement to surface in rocks STZ ranging from Precambrian to Cretaceous age FM and is associated with a characteristic pattern Sediment PRAA of alteration which includes native sulphur, Ce-phosphate and Ce-carbonate minerals, and Thickness microcrystaline quartz and quartz microvein- Km lets (Abercrombie and Feng, 1996). 0 Geology 1 MLE 2 The stratigraphic column at Fort MacKay is only about 300-350 m thick (Fig. 3 2). Basement comprises Precambrian grani- 4 SA toid gneisses which have undergone oxidative 5 alteration to variable depths beneath the sub- 6 Devonian unconformity. An Early to Middle Devonian red bed-evaporite-carbonate se- 7 quence, the Elk Point Group, lies unconfor- mably on basement and comprises regolith, Figure 1. Total sediment thickness and principal structural elements of the Western Canada Sedimentary Basin and lower and upper red bed-salt sequences (solid lines) and underlying PreCambrian basement (dashed lines). PP - Pine Point; FM - fort MacKay; with an intervening dolostone containing or- GSLZ - Great Slave lake Shear Zone; STZ - Snowbird Tectonic Zone; TA - Tathlina Arch; PRAA - Peace ganic-rich marine laminites. The Elk Point River - Athabasca Arch; MLE - Meadow Lake Escarpment; SA - Sweetgrass Arch.

May 1996 1 1995–1996 MDD EXECUTIVE The Gangue No. 52

Following are the MDD Executive and Directors for the 1995-1996 term. Please contact The Gangue is published quarterly by the Mineral Deposits Division, GAC, and is distrib- any of these individuals for enquiries, or to suggest initiatives for MDD. uted to members as part of their membership.

Chairperson: Jennifer Pell Indian and Northern Affairs MDD Goals and Objectives & Membership: 4-4914 50th Street, Bellanca Bldg. P.O. Box 1500, Yellowknife, NWT, X1A 2R3 Tel: 403-669-2640 FAX: 403-873-5763; The Mineral Deposits Division of the Geo- e-mail: [email protected]. logical Association of Canada is Canada’s fore- most society for promoting the study of mineral deposits by supporting local and national meet- Vice-Chairperson: Cominco Resources International Ltd., ings, symposia, short courses and field trips. We David Moore 7th Floor 409 Granville St. Vancouver, B.C., V6C 1T2. sponsor the publication of research relating to ore Tel: 604-685-3064; FAX: 604-685-3069 deposits and metallogeny and recognize the con- tributions of outstanding Canadian economic ge- Past-Chairperson: Dept of Natural Resources ologists by annually awarding the Duncan Derry H. Scott Swinden P.O. Box 698, Halifax and William Harvey Gross medals and the Julian Nova Scotia, B3J 2T9 Boldy certificate. Tel: 902-424-8135 FAX: 902-424-7735; e-mail: [email protected]. Publication Schedule: Secretary: Inmet Mining Corporation SUBMISSION PUBLICATION Gary S. Wells 3-311 Water Street, Vancouver, B.C., V6B 1B8 Tel: 604-681-3771 FAX: 604-681-3360 DEADLINE DATE December 15 January Treasurer: Cathro Exploration Corp. March 15 April Robert J. Cathro RR#1, Site U-39, Bowen Isl., B.C., V0N 1G0 June 15 July Tel: 604-947-0038 FAX: 604-947-0038 September 15 October Publications: Consulting Geologist Kathryn P.E. Dunne RR#1 S12 C16 Information for contributors: Gabriola Island, BC, V0R 1X0 Tel: 604-247-7432 FAX: 604-247-7458; The objective of this newsletter is primarily e-mail: [email protected]. to provide a forum for members and other profes- sionals to voice new ideas, describe interesting Professional Development New Brunswick Geological Surveys Branch mineral occurrences or expound on deposit mod- Short Courses: P.O. Box 50, Bathurst, N.B., E2A 3Z1 els. Articles on ore deposits, deposit models, news Tel: 506-547-2070 FAX: 506-547-7694 events, field trips, book reviews, conferences or David R. Lentz other material which may be of interest to the economic geology community are welcomed. Re- Professional Development BC Geological Survey prints of presentations given to companies, min- Field Trips: 5100 - 1810 Blanshard Street; Victoria, BC, V8T 4J1 ing groups or conferences are particularly Dani Alldrick Tel: 604-952-0412 FAX: 604-952-0381; welcome. e-mail: [email protected] Manuscripts should be submitted on IBM- formatted diskettes in any major word processor Program Chair:Winnipeg ‘96 Falconbridge Limited format. A printed version should be included. D. James Robertson 21 Murray Park Road; Winnipeg, Manitoba, R3J 3S2 Illustrations must be camera-ready; photos should Tel: 204-837-3614 FAX: 204-885-4152 be of good quality. Short items dealing with news events or meetings can be submitted by FAX, Program Chair: Ottawa ‘97 Mineral Resources Division, GSC, 601 Booth St., postal mail or E-mail. Al Sangster Ottawa, Ont, K1A 0E8. Tel: 613-992-8603; FAX: 613-996-9820; e-mail: [email protected]. Contributions may be edited Newsletter Editor The Gangue, c/o:Box 8076, Victoria, B.C., V8W 3R7 for clarity or brevity. Brian Grant Tel: 604-952-0454; FAX: 604-952-0451 For Information & Submissions: e-mail: [email protected] Brian Grant MDD DIRECTORS Editor - THE GANGUE Isabelle Cadieux (1995-1998) Quebec, Quebec PO Box 8076, Victoria, BC, V8W 3R7 Tel: 418-688-4272; FAX: 418-688-4272 Tel: 604-952-0454 FAX: 604-952-0451 Dan Brisbin (1995-1998) Timmins, Ontario. E-Mail: [email protected] Tel: 705-267-1188 Michael J. Downes (1995-1998) Toronto, Ontario. Tel: 416-869-3578; FAX: 416-869-3359. Dani Alldrick - Associate Editor Grant Abbott (1993-1996) Whitehorse, Yukon E-Mail: [email protected] Tel: 403- 667-8510 FAX 403- 667-7074 *** Benoit Dubé (1993-1996) Sainte-Foy, Quebec Tel: 418- 654-2669 FAX: 418- 654-2615; The MDD encourages geoscientists to join e-mail: [email protected]. the division and contribute to the various Jenna Hardy (1993-1996) Vancouver, British Columbia programs and activities. Tel: 604-684-1175 FAX: 604-684-0147 Terence J. Bottrill (1994-1997) Oakville, Ontario Tel: 905-842-2893 Pamela L. Schwann (1994-1997) La Ronge, Saskatchewan Tel: 306-425-4564 FAX: 306-425-2909 Marcos Zentilli (1994-1997) Halifax, Nova Scotia Tel: 902-494-3873 FAX: 902-494-6889

2 The Gangue No. 52 have carried metals derived from basement or the Elk Point Group. These brines may be original residual evaporite brines, or they may have originated as low salinity waters of me- Alberta Saskatchewan teoric origin which rose to salinities approach- Athabasca ing halite saturation by dissolution of salt in River the Prairie Formation. In either case, reaction

Au with anhydrite and hematite in red bed-eva- porite strata of the Elk Point Group would Au Au 500 m have raised redox potential of the brine suffi- Au Basement ciently to leach and transport Au and other metals. Au Precambrian BasementQuaternary Colorado Gp Precipitation of Prairie-type mineraliza- Prairie Salt Mannville Gp Au tion from oxidized brines occurs as these Wabamun brines flow across major redox boundaries Winterburn Gp and may be further affected by depressuriza- Meteoric waters Woodbend Gp tion and cooling. Redox is controlled region- Formation waters Beaverhill Lake Gp ally at stratigraphic interfaces between red Oxidizing brines Elk Point Gp Deep brines bed-evaporite sequences and marine carbon- 50 km Precambrian ates, and locally by faults and fracture systems which provide conduits to move saline, oxi- dized fluids vertically into reduced, organic- bearing marine limestones. In the absence of bacteria and at temperatures such as those en- Figure 2. Cartoon showing possible sites for precipitation of Prairie-type mineralization in the Fort MacKay countered in northeastern Alberta (below region. Preferred sites are at major redox boundaries. Deep drilling in the Fort McMurray area confirms 90°C) redox reactions are slow and are not the presence of saline brines in fractured granites below the WCSB. Faulting is shown schematically (from capable of controlling redox conditions. If, Abercrombie, 1996). however, bacteria are present, these reactions proceed extremely rapidly and cause signifi- examination. Sample preparation initially in- peratures, native S forms through reduction of cant local variation in redox conditions pro- volved production of doubly polished uncov- SO4(aq) by reaction with microbially produced moting precipitation of oxyhalide-complexed ered thin sections and singly polished chip H2S(g). Native S occurs where sulphate-rich metals. The presence of hydrocarbons (or mounts. During the polishing process mi- brines have interacted with organic material other organic material) and their oxidation by crodisseminated minerals were plucked and (hydrocarbons and/or dispersed organic mate- microbially mediated redox reactions are removed from the polished surface. Conse- rial). Thus, native S formation records reduc- therefore critical factors in the formation of quently, most observations have been made on tion of oxidized brines accompanied not by Prairie-type mineralization. broken surfaces. This modified procedure is sulphide formation, but by sulphide oxida- References successful in preventing the loss of microdis- tion. Although it remains to be tested by geo- seminated particles in the preparation stage. chemical modeling, this may provide an ex- Abercrombie, H.J., 1996. Prairie-type Au-Ag-Cu. In D. Loss of microdisseminated mineralization planation for the abundance of Lefebure (Coordinator), New Mineral Deposit Mod- during polishing is consistent with occurrence microdisseminated native metals and alloys, els for the Cordillera, 1996 Cordilleran Round-Up of metallic phases within the porous network, and lack of sulphides observed in mineralogi- Short Course Notes, B.C. Geological Survey,p.J1- J20. as determined by SEM imaging. cal examinations. The presence of Ag-, Pb-, Abercrombie, H.J., and Feng, R., 1994. Gold and PGE Summary of Mineralization Bi-, Cu-, and Fe-chlorides, and an observed anomalies in Phanerozoic sedimentary rocks, north- and Alteration association between Au and NaCl, indicate eastern Alberta - potential for new deposits? Program that Cl is a major component of mineralizing and Abstracts, Calgary Mining Forum, Calgary Min- Prairie-type mineralization is charac- solutions. eral Exploration Group Society, Feb. 10-11, 1994, p. terized by microdisseminated Au, Ag, Cu and Genesis of Prairie-Type Mineralization 51. a wide variety of other native elements, inter- Abercrombie, H.J. and Feng, R., 1996. Geology of Prairie- grown metals, and metal alloys. Mineralogi- The formation of anomalous occurrences type Au-Ag-Cu mineralization, Fort MacKay region, cal studies by the GSC and other workers have northeastern Alberta. In R.W. Macqueen (ed.), Final of Prairie-type Au-Ag-Cu and related miner- Report, Canada-Alberta Mineral Development established the presence of a large variety of alization at Fort MacKay is illustrated in car- Agreement, Geological Survey of Canada Bulletin, in native metals and metal intergrowths and/or toon form in Figure 2. It is suggested that press. alloys including: Cu-Zn, Cu-Fe-Zn, Au-Cu, metals probably originated in the PreCam- Bloom, M.S., Gilbert, D.J., Gammons, C.H., and Wilde, Au-Cu-Zn, Au-Ag, and Fe-Ni-Cr. Prelimi- brian basement, although research by Thiede A.R., 1992. Reaction path modeling for hydrothermal nary work has also revealed the presence of (1975) showed the Cu, Pb, and Zn contents of Au-PGE mineralization at CoronationHillandsimilar novel elemental associations Au-Ca, Au-Si, Elk Point Group lithologies to be anomalously deposits of the South Alligator Mineral Field, Austra- lia; in Water-Rock Interaction, (ed.) Y.K.Kharaka and and Au-Al, although these results await con- enriched compared to other evaporite basins A.S. Maest, Balkema, Rotterdam, p. 1569-1573. firmation. worldwide, indicating that the source of met- Feng, R. and Abercrombie, H.J., 1994. Disseminated Au- Of the samples examined, the most abun- als may not be restricted to basement rocks. Ag-Cu mineralization in the Western Canada Sedi- dant Au and related mineralization is in the Brine composition, redox state, and pH mentary Basin, Forth MacKay, Northeast Alberta: A Waterways Formation of the Late Devonian new gold deposit type; in Current Research 1994-E; control the solubility of Au, Ag, and Cu and Geological Survey of Canada, p. 121-132. Beaverhill Lake Group (Fig. 2) where Au oc- other metals in saline brines (e.g., Jaireth, Jaireth, S., 1992. The calculated solubility of platinum and curs in association with native Ag, Cu, Zn, Pb, 1992). If reducing formation waters react first gold in oxygen-saturated fluids and the genesis of Cd, Fe, Cr, Ni, Sb, and Bi. Gold is next most with sulfate-rich evaporates (anhydrite) and platinum-palladium and gold mineralization in the abundant in basement rocks where it is asso- then with a typical red-bed assemblage unconformity-related uranium deposits; Mineralium ciated with Ag, Cu, Pb, Sb, Sn, W, and Cl. (hematite), oxygen fugacities well into the Deposita, v. 27, p. 42-54. These preliminary results show that gold and hematite field can be attained (Bloom et al., Thiede, D.S., 1975. Geological implications of variation in related mineralization are least abundant in heavy metal content in the Elk Point evaporite se- 1992). Under these conditions, Au, Ag, Cu quence, Saskatchewan, Canada; M.Sc. thesis disser- the Basal Red Beds (Elk Point Group) and and other metals, including platinum group tation, University of Wisconsin -Madison, Cretaceous sandstones. elements, are soluble as chloride complexes. unpublished, 192 p. Native S has been observed in all units High salinity (350 g/l) brines are known from except Cretaceous sandstones. At low tem- the Elk Point Group and these are inferred to

May 1996 3 China’s Jinchuan Ni-Cu deposit Mineral Deposits Division By Dr. Gang Chai

Jinchuan Ni-Cu deposit in China, with a La Paz reserve of over 500 million tones grading 1.2 BOLIVIA wt% Ni and 0.7 wt% Cu, is presently the third Oruro largest Ni deposit in the world. The deposit is Arica Potosi hosted in an ultramafic igneous body, intruded in the southwest margin of Sino-Korea plat- form about 1500 million years ago. The intru- Jujuy sion is about 6 km long, 350 m wide and Antofagasta extends more than 1100 m down dip. Salta San Miguel There are three lobes in the Jinchuan Copiapo de Tucuman intrusion, namely west, west-central and east. The two western lobes are narrow and tabular CHILE Cordoba in shape. A lateral zonation of rock types is present, with dunite at the core, grading Mendoza Rosario through lherzolite to olivine pyroxenite at the Santiago Buenos Aires margins. Sulfide mineralization also coin- November 9-29th , 1996 cides with the zonation, with Ni, Cu and PGE ARGENTINA increasing from the margins towards the cen- Tour Leader Al Sangster, of the Geological • The tour will wrap up with a free day in tre, and ore textures from disseminated to net- Survey of Canada, has organized an adventur- Santiago. textured sulfides. The eastern lobe is V- ous 3-week field trip through the remarkable A detailed itinerary is available on request shaped and is characterized by layering in geology and mineral deposits of southern Bo- (FAX request to 604-952-0381) which dunite occurs at the base and grades livia, northern Argentina and northern Chile. Lecture sessions on regional geology and ore Dates:This tour departs from Toronto or upwards into lherzolite, plagioclase lher- deposits will complement the tour. Vancouver Saturday, November 9/96, and zolite, and then lherzolite again at the top. returns to Toronto or Vancouver Friday, BOLIVIA: Epithermal & transitional Au de- November 29/96. Sulfides occur at the base of this chamber, and posits, Ag-Sn-Pb-Zn veins & the world’s larg- Ni and Cu grades decrease upward. est Ag deposit Number of Participants:Maximum The igneous rocks consist primarily of ARGENTINA: SEDEX Pb-Zn-Ag deposits, number of participants is 25. Minimum for this tour is 15. Preference will be given to cumulus olivine with varying amount of inter- and transects of the Altiplano and the Andes. MDD members. stitial pyroxene, plagioclase or sulfide. Major, CHILE: Epithermal, skarn and manto gold de- trace and rare earth element data show linear posits, porphyry and manto-style copper de- Cost: Costs have not been finalized but posits, lithium & nitrate playa deposits and cost per participant will be in the order of correlations between MgO and most other ele- $4800CDN. This includes return air travel ments, confirming olivine is the only cumulus magnetite flows in spectacular Andean volcano country costs from Toronto or Vancouver, all local silicate mineral. Olivine in the Jinchuan intru- travel, accommodation, breakfasts, some sion has a forsterite content around 83-85%, Highlights include: other meals, plus the Field Trip Guidebook. $500 deposit required with application. corresponding to a calculated • Tours of the Laurani, Korri Kollo and San MgO/(MgO+FeO) ratio for the primary Jose mines and a full-day tour of Cerro TO APPLY: magma of 0.64, which, in turn, indicates an Rico de Potosi. MgO content for this magma of about 12 wt%. • Send your name, full mailing address, tele- A guided road trip through the Altiplano, phone and FAX numbers to the following It is concluded that: 1) the Jinchuan in- with geo-stops and a full-day tour of Mina address. Cheques in the amount of Aguilar. Cdn$500.00 should be payable to “MDD trusion represents the ultramafic cumulates of • a high-MgO basaltic magma; 2) the western The geological road tour then heads west Central Andes Field Trip”. across the Andes passing within the shadow Dani Alldrick parts of the Jinchuan intrusion are the major of an active volcano. conduits of the original magma; the rocks and MDD Field Trip Coordinator • The journey will continue through the Ata- ores are formed as a result of a flow differen- c/o BC Geological Survey cama Desert with visits to the El Laco 5 - 1810 Blanshard Street tiation process; the eastern part represents a magnetite flows, Li-salars, nitrate deposits, higher level in the magma chamber where Victoria, BC, CANADA, V8V 1X4 geothermal fields, recently active volcanic Tel: 604-952-0412 FAX: 604-952-0381 crystallization occurred in response to magma fields and tours of the Mantos Blancos, E-mail: [email protected] convection with periodic replenishment; 3) Chuquicamata, Mina Sur and Escondida after consolidation, the upper portion of the mines. intrusion, which would have gabbroic compo- • From Copiapo the group will tour the Can- sition, has been eroded away. delaria and Punta del Cobre mines and the Refugio and La Coipa mines in the The volume of the original magma for Maricunga district. the Jinchuan intrusion should be considerably • Lecture sessions are planned at La Paz, Ju- larger than the present ultramafic body, and juy and Antofagasta. Visits have also been deep faults in the Jinchuan area should lead to arranged to the Museum at Antofagasta and more than one site of nickel concentration. Lake Titicaca. Free time has been sched- Therefore, good exploration potential exists uled in La Paz and at the regional centres of Salta, Antofagasta and Copiapo. in Jinchuan region.

4 The Gangue No. 52 THE DISCOVERY AND EXPLORATION OF KIMBERLITES ON THE BHP / DIA MET CLAIMS, LAC DE GRAS REGION, NORTHWEST TERRITORIES, CANADA

by J.A. Carlson, M.B. Kirkley and R.M. Ashley - BHP Minerals Canada Ltd. A total of fifty seven-kimberlites have isochron yielded an Eocene age of 52 Ma for collected in the vicinity of Blackwater Lake been discovered on the BHP / Dia Met claim phlogopite within one of the kimberlites. near the Yukon / Northwest Territories border. block (“Exeter Lake Property”) located 300 Till is the most extensive glacial deposit A helicopter-supported regional sam- kilometers NNE of Yellowknife, Northwest pling team gradually tracked the indicator Territories, Canada. This paper briefly de- in the Lac de Gras area and correlates with late Wisconsinan Laurentide ice. Glaciofluvial mineral train 300 km eastward to the Lac la scribes the regional setting and geology of the Martre area. Dia Met then took over funding kimberlites and summarizes the exploration deposits are widespread and take the form of eskers and related kames. Glacial transport of the exploration program in 1984. By 1985, history and methods used by the BHP / Dia sampling had been undertaken as far as the Met joint venture. likely flowed first to the southwest, followed by flow to the west and most recently by flow Aberdeen Lake area, 900 km east of the west- Geological Setting and Characteristics to the northwest. ern edge of the Slave craton. Three highly of the Kimberlites anomalous heavy mineral samples were iden- The Exeter Lake property kimberlites are tified immediately north of Lac de Gras, and The Lac de Gras kimberlites intrude the distinctive when compared with the kimber- of great significance was the lack of anoma- Slave Structural Province, one of several lite pipes of South Africa because many con- lous samples to the east of the Lac de Gras Archean cratons which represent continental tain preserved crater deposits. Crater facies area, which suggested the source area had nuclei for the geological evolution of North lithologies include ash tuffs, lapilli tuffs, and been located. Extensive higher density sam- America. The Slave is a relatively small cra- lithic tuffs, as well as kimberlitic mudstones, pling was undertaken in the northeast and ton (180,000 km2) with an extensive and siltstones and sandstones. Unsorted to weakly west of Lac de Gras, refining the extent of the unique history. In addition to containing the sorted beds are commonly visible. Non-kim- anomalous glacial sediments. earth’s oldest known rocks (3.96 Ga), the berlitic clay, silt and gravel layers have been Dia Met began to acquire ground in 1989 Slave differs significantly from younger observed at depths of over 100 meters within and in the following year an extremely anoma- Archean granite-greenstone terranes in its some of the craters and wood fragments are lous sample was taken from the north shore of constituent rocks and contacts with bordering common in many of the crater deposits. Dia- a circular, crater-like lake named Point Lake. Proterozoic orogenic belts. Recent multidis- treme facies kimberlite is typically fragmental The dataset of indicator mineral geochemistry ciplinary studies have produced compelling with substantial host rock contamination in within the existing claim area was evaluated evidence favouring a subduction-accretionary some cases. Hypabyssal kimberlites on the independently by John Gurney and Rory model for the formation of the Slave craton property have mineral assemblages compara- Moore who concluded that the indicator min- (e.g. Davis et al., 1994). ble to Group I South African kimberlites. erals originated from highly diamondiferous Archean rocks within the property area Discovery of Kimberlites kimberlitic sources. Dummett, then BHP’s can be divided into three broad lithostrati- in the Northwest Territories North American Exploration Manager, led graphic groups: metasedimentary schists, BHP to sign the joint venture agreement with migmatites and various syn- and post-tectonic The largest staking rush in Canadian Dia Met on September 5, 1990. Additional intrusive complexes. Five Proterozoic dike mining history was initiated by the discovery claims were subsequently staked and the joint swarms with ages ranging from 2.4 - 1.27 Ga of diamonds in the Point Lake kimberlite pipe venture property presently consists of nearly intrude the Archean sequence. Diabase and in late 1991. This discovery was the result of 350,000 hectares within two claim blocks. gabbro dikes vary from 5 to 100 metres wide systematic heavy mineral sampling over a ten In May 1991, a BHP geophysical crew and may extend for hundreds of kilometers. year period and covered an east-west distance surveyed a grid over Point Lake and results of about 1200 km across the Northwest Terri- from the ground survey enabled Dummett of Kimberlites are the only Phanerozoic tories (NWT). Evaluation of the Mountain BHP to successfully target the discovery drill rocks known in the Lac de Gras region, al- diatreme located in the MacKenzie Moun- hole in September of that year. The ensuing though fossil-bearing mudstone xenoliths tains, western NWT, was being conducted in announcement that 81 diamonds (16 0.5mm, within the kimberlite indicate that sediments 1981 as part of a joint venture program be- 65.5mm) had been recovered from 59 kg of must have formed a thin veneer over the older tween Superior Minerals, Falconbridge and kimberlite core, and subsequent reverse circu- rocks at the time of kimberlite emplacement. CF Minerals under the direction of Hugo lation drilling sparked the staking rush. Ap- Fossils from the xenoliths include dinoflagel- Dummett (Superior). De Beers’ subsidiary proximately 20 million hectares of the Slave lates, pollen, spores, wood and teleost fish Diapros and other diamond exploration com- craton have now been staked for diamonds, parts and provide evidence that the kimber- panies were active south of Norman Wells. and in addition to BHP and Dia Met, major lites were emplaced in early Tertiary time As part of this evaluation, garnets and chro- companies including De Beers, Kennecott and (Nassichuk and McIntyre, 1995). An Rb/Sr mites were recovered from a series of samples Ashton are involved along with numerous smaller companies. The Point Lake pipe was bulk sampled by 37 reverse circulation drill holes (15 cm 1997 diameter) during January to March, 1992. The sample returned a grade of 0.63 carats per th dry metric tonne but is currently considered 50 ANNIVERSARY of the sub-economic because of relatively low stone quality. Since the discovery of the Point Lake pipe, an additional 56 kimberlites have been Geological Association of Canada discovered on the Exeter Lake Property. Plan to Join the Celebration at Ottawa '97! Exploration Methods and Results The early stages of exploration for dia- monds in the NWT consisted of territory-wide

May 1996 5 Bulk Sampling Results for four planned Production Pipes: lines from ground geophysics provide a means for designing reverse circulation drill PIPE TOTAL TONNES TOTAL CARATS SAMPLE GRADE AVG. VALUE hole (15 and 27 cm bit diameter) patterns to NAME SAMPLED RECOVERED CARATS/TONNE US$ PER CARAT obtain representative initial bulk samples without the need for delineation core drilling. Panda 3,402 3,224 0.95 $130 The samples (typically 50 to 200 tonnes) are Misery 1,030 4,313 4.19 $26 processed in a 10 tonne per hour dense media Koala 1,550 1,465 0.95 $122 separation plant which was constructed on Fox 8,223 2,199 0.27 $125 site. Seventeen of fifty seven kimberlite pipes have been bulk sampled to date. Large bulk samples up to about 7000 ton- regional heavy mineral sampling from fluvial kimberlite/non-kimberlite target discrimina- nes have been processed on site from under- and glaciofluvial sediments on a scale of tens tion and estimates of pipe size. ground workings and large diameter reverse of kilometers. Initial ground geophysical test Core drilling programs have been used to circulation drilling programs for more accu- surveys pinpointed the target under Point confirm nearly all of the 57 kimberlites on the rate estimation of diamond grade and quality. Lake and prompted the flying of the entire Exeter Lake Property and have provided sam- Reserve estimates have been refined through property with helicopter-borne total field ples for microdiamond and kimberlite indica- delineation core drilling. Commercial quan- magnetics (TFM), electromagnetics (EM), tor mineral analysis. Targets were drilled with tities and qualities of diamonds have been in- and very low frequency electromagnetics an eighty percent success rate and in most dicated for five pipes on the Exeter Lake prop- (VLF). The numerous targets defined from cases with a single hole that also provided a erty and the project is currently at final the airborne geophysics were prioritized for check on the interpreted perimeter outlines. A feasibility stage. drilling by collecting till samples at 250 m few of the kimberlites crop out and were con- Summary intervals along lines perpendicular to the firmed by geological mapping, and therefore dominant ice flow direction. The extent and were sampled from outcrop. However, most Discovery of the diamondiferous Lac de chemistry of the indicator mineral (pyrope of the known pipes are overlain by lake water Gras kimberlite field resulted from the sys- and eclogitic garnets, chromites, ilmenites, and glacial sediments. tematic application of the heavy mineral chrome diopsides) dispersion trains were method and helicopter geophysics. Diamond evaluated. Ground geophysics including Kimberlite pipes are selected for initial grades and qualities have been confirmed TFM, EM, VLF, gravity, seismic and ground bulk sampling primarily based on mi- through a series of bulk samples. penetrating radar have enabled more precise crodiamond and indicator mineral analyses of the core or surface samples. Perimeter out- The location of the Lac de Gras kimber- lite field in the central portion of the Slave craton is virtually analogous to the position of the Kimberley field in the Kaapvaal craton. Differences of the Kimberley pipes to the Lac de Gras pipes may be related mostly to erosional level. The Lac de Gras field is con- siderably younger than the Kimberley pipes and has experienced less erosion. Crater, dia- treme and hypabyssal facies have all been de- scribed for the Exeter Lake property kimber- lites. A total of fifty-seven kimberlite pipes have been identified on the Exeter Lake Prop- erty and seventeen have been bulk sampled. A proposed development plan is in place for the first five kimberlite mines including Panda, Misery, Koala, Fox and Leslie, with a projected mine life of twenty-five years. References Carlson, J.A., Kirkley, M.B., Ashley, R.M., Moore, R.O. and Kolebaba, M.R. (1995) Geology and exploration of kimberlites on the BHP / Dia Met claims, Lac de Gras region, Northwest Territories, Canada. In Ex- tended Abstracts Vol., Sixth International Kimberlite Conference, Novosibirsk, Siberia, p. 98 - 100. Davis, W.J., Fryer, B.J. and King, J.E. (1994): Geochemis- try and evolution of Late Archean plutonism and its significance to the tectonic development of the Slave craton. Precambrian Research, 67, p 207-241. Fipke, C.E., Dummett, H.T., Moore, R.O., Carlson, J.A., Ashley, R.M., Gurney, J.J. and Kirkley, M.B. (1995): History of the discovery of diamondiferous kimber- lites in the Northwest Territories, Canada. In Extended Abstracts Vol., Sixth International Kimberlite Confer- ence, Novosibirsk, Siberia, p 158 - 160. Nassichuk, W.W. and McIntyre, D.J. (1995): Cretaceous and Tertiary fossils discovered in kimberlites at Lac de Gras in the Slave Province, Northwest Territories. In Current Research 1995-B, Geological Survey of Can- ada, p 109-114.

Figure 1. Map showing the geological setting of the BHP / Dia Met Exeter Lake Property.

6 The Gangue No. 52 MEETINGS, WORKSHOPS & FIELDTRIPS

[Editor’s Note: If you are aware of an 29 July - 2 Aug Proterozoic Evolution in the Vancouver, B.C. Sponsored by Randol Inter- event of potential interest to economic geolo- North Atlantic Realm. Aurora Hotel (709- national Ltd. Conference & exhibition. 896-3398) & Labrador Inn (709-896-3351), Contact: Randol, 21578 Mountsfield Drive, gists please FAX a note to (604) 952-0451, or Goose Bay, Labrador, NFLD. Conference & Golden, CO 80401. Tel: 303-526-1626; an Email to [email protected] so that field trips. Contact: C.F. Gower, Newfound- FAX: 303-526-1650. it may be included in the next issue of The land Dept of Natural Resources, P.O. Box Gangue. Notices must include a contact ad- 8700, St. John’s, Newfoundland, A1B 4J6. 27 - 29 Nickel ‘96 - Mineral to Market.Kal- dress or phone number. Thanks!] Tel: 709-729-2118; FAX: 709-729-3493; goorlie, Australia. Sponsored by the Email: [email protected]. Australasian Institute of Mining & Metal- lurgy, Australian Institute of Geoscientists, May 1996 and W Australian School of Mines. Contact: August 1996: Dr. Eric Grimsey, WA School of Mines, Box 20 - 22 The World of Giant Mineral Deposits. 597, Egan St., kalgoorlie, WA 6430, Austra- 3-day short course with lab. Univ. of Mani- 4-14 30th International Geological Con- lia. Tel: 090-80-5182; FAX: 090-80-5181. toba, Winnipeg, Manitoba. Contact: Peter gress. Beijing, China. For information on Laznicka, Dept of Geol Sciences, Univ of this major international event contact: Prof. January 1997 Manitoba, Winnipeg, MB, R2M 5C9. Tel: Zhao Xun, Deputy Secretary General, 30th 204-474-6909; FAX: 204-257-3917; e-mail: IGC, PO Box 823, Beijing 100037, P.R. 8-11 IGCP 356 & Mineral Deposits Studies [email protected]. China. Tel: 86-10-8327772 or 86-10- Group Meeting. Univ. of Glasgow, Scot- 8323188; FAX: 86-10-8328928; land. Fee £30, reduced fees for members & 22 - 24 3rd Annual African Mining Invest- Email: [email protected]. ment & Business Opportunities. Hilton students. Contact: A.J. Hall, Dept of Geol- Bonaventure, Montreal, Quebec, Canada. 44 ogy & Applied Geology, Univ. of Glasgow, African nations invited. Sponsored by World September 1996 Glasgow G12 8QQ. E-mail: ajh@geol- Bank Multilateral Investment Guarantee ogy.gla.ac.uk. 3-6Minerals, Metals & the Environment II. Agency in cooperation with CIDA, Northern 13 - 15 Mexico Mining ‘97. Conference & Ex- Miner & PDAC. Presentations on areas Agricutural University, Suchdol, Prague. Contact: The Conference Office, IMM, 44 hibition. Puerto Vallarta, Mexico. Contact: available for exploration/development. Con- L. Feeney, Randol International Ltd., Gold- tact: K. Millett, MIGA/World Bank, 1818 H Portland Place, London W1N 4Br, England. Tel: +44-171-580-3802; FAX: +44-171- en Colorado, USA. Tel: 303-526-1626; Street NW, Rm U12-367, Wash., DC 20433, FAX: 303-526-1650. USA. Tel: 202-473-0394; FAX: 202-522- 436-5388. 2650. 22 - 25 Association of Earth Science Editors April 1997 30th Annual Meeting. Sudbury, Ontario. 24 - 26 Trace Element Geochemistry of Vol- International meeting hosted by the Ontario 21 - 25 EACM ‘97: East Asian Continental canic Rocks: Applications for Massive Ministry of Northern Development & Sulphide Exploration. GAC/MAC Annual Margin - Geology and Development. Hong Mines. For details contact: Publications Kong. Sponsored by Univ. of Hong Kong, Meeting Short Course, Univ. of Manitoba, Services Section, 933 Ramsey Lake Road, Winnipeg. Sponsored by the Mineral Depos- H.K. Geological Survey, & Geological So- Sudbury, Ontario, P3E 6B5. Tel: 705-670- ciety of Hong Kong. Contact: EACoM ‘97, its Division - GAC. Contact: D. Lentz, NB 5765; FAX: 705-670-5770. Geological Survey, Tel: 506-547-2070; or, Earth Sciences Dept, Univ. of Hong Kong, D. Wyman, Univ. of Sask. Tel: 306-966- 26 - 28 Mesozoic Geology of the Eastern Aus- Pokfulam Road, Hong Kong. FAX: 852- 5683. tralia Plate. Sheraton Brisbane Hotel & 25176912; Email [email protected]. Towers, Brisbane, Queensland. Geological 24 - 26 Undersaturated Alkaline Rocks. evolution & economic potential of Mesozoic September 1996 MAC Short Course, GAC/MAC Annual rocks. Contact: Natlie O’Sullivan, Event Or- Meeting, Univ. of Manitoba, Winnipeg. ganizer, PO Box 1280, Milton, Queensland Aug 30 - Sept 5 Large Meteorite Impacts and Contact: Bill Brisbin, Dept Geol. Sci, Univ 4064, Australia. Tel: 61-7-3369-0477; FAX Planetary Evolution. Sudbury, Ont., Can- of Manitoba, Winnipeg, Manitoba, R3T 61-7-3369-1512 ada. 3 days of talks plus fieldtrips. Contact: 2N2. Tel: 204-474-7343; FAX: 204-261- Dr. B.O. Dressler, Lunar & Planetary Insti- 7581;Email: [email protected]. October 1996 tute, 3600 Bay Area Boulevard, Houston, 28 - 31 NABRE - Proterozoic Sequence Stra- Texas, USA, 77058-1113. Tel: 713-486- tigraphy Field Workshop. Gunpowder 2112; Fax: 713-486-2162; Email: 8-11 Large & Extra Large (Unique) Deposits [email protected]. nasa.gov. Resort, Northwest Queensland, Australia. of Rare & Precious Metals Symposium. Includes day of lectures & exercises, basin St. Petersburg, Russia. Organizers: numer- analysis, seismic & well log interpretations, ousRussian professional groups. Includes January 1998 plus field evaluation of geology and data. discussions on distribution, genesis, ore con- Fee $1100 Aus includes accommodation & trols, exploration technologies, metallogeny. 28 - 30 Exploration Methods ‘98 - Pathways meals. Contact: Algis Juodvalkis, AGSO, Contact: Prof. Y.B. Marin, St. Petersburg to Discovery. Vancouver, BC. Sponsored by GPO Box 378, Canberra, ACT 2601. Tel: State Mining Institute, 21st Line, 2 V.O., St. the BC&YCM, SEG, BCGS, GSC. This will +61-6-249-9823; Fax +61-6-249-9983. Petersburg, 199026, Russia. Tel: 812- be a special version of the traditional Cordil- 2188247; FAX: 812-2132613; E-mail: leran Roundup. Contact: G. Carlson, ConSil Corp., Suite 500 - 625 Howe Street, Vancou- June 1996 [email protected].; http:// www.ripn.net/relarn/ members/ vmo/ ver, BC, V6C 2T6. FAX: 604-331-0845. 13 - 23 Volcanoes & History: Italian/Sicily reg_eng.html Field Trip. Base cost about $2,500 US. Con- Future GAC/MAC Meetings: tact Alan Jacobs, GEOPROBE, 7125 November 1996 May 1996 Saltsburg Road, Pittsburgh, PA 15235-2297. Tel: 412-793-6115 or Email: AJa- 6-29Mineral Deposits Division - Bolivia - 27 - 29 Winnipeg ‘96. GAC/MAC Joint An- [email protected]. Chile - Argentina Field Trip. Join the nual Meeting. Winniper, Manitoba. Details: MDD in La Paz, Bolivia for another of the G.S. Clark, General Chair, Dept. of Geologi- renowned MDD fieldtrips. Dr. Al Sangster, cal Sciences, Univ. of Manitoba, Winnipeg, July 1996 GSC, Ottawa will be the trip leader. For de- Manitoba, R3T 2N2. Tel: 204-474-8857. tails see ad this issue or contact: Dani 4-5 Short Course on Basin Processes & Pb- Alldrick, MDD Fieldtrip Coordinator, Tel: May 1997 Ottawa ‘97. GAC/MAC Joint An- Zn Ore Deposits. Univ. of Ballarat, 604-952-0412; FAX: 604-952-0381; Email: nual Meeting. Ottawa Congress Centre, Ballarat, Victoria, Australia. Contact: D. [email protected]. Ottawa, Ontario. Details: Secretariat, c/o Arne, P.O. Box 663, Ballarat, Victoria 3352, GSC, Rm. 757 - 601 Booth Street, Ottawa, Australia. FAX: 61-53-279144; Email: 12 - 15 Vancouver ‘96: Global Mining Oppor- Ont., K1A 0E8. Tel: 613-947-7649, FAX: [email protected]. tunities. Westin Bayshore Hotel, 613-947-7650, Email: [email protected]

May 1996 7 International Mining Highlights

• Russia’s aluminium industry has been, and mineral leasing procedures and property Aug/95 paved the way for foreign invest- continues to be, dependant upon large valuation techniques, among other topics. ment into mining and eliminated preferen- quantities of imported raw materials. Ex- A Montana law firm, who hosted the dele- tial treatment for state-financed compa- ports, however, have surged from 123 500 gation, planned to conduct a mineral title nies. Participation of a Brazilian company tonnes in 1990 to an estimated 2.2 million seminar in Beijing in March. (NWMA Bull is still required but the company can now tonnes last year. While there is little doubt vol 101, #2) be foreign owned, with at least one Brazil- ian director. The new rules have led to a that significant imports of raw materials • Major porphyry-Cu deposits of the Cordil- will continue over the next few years the mini-boom in gold exploration in South lera are usually linked to the Tertiary pe- America’s largest country. (NM 11/03/96) London-based Metal Bulletin Research an- riod. Recent research undertaken between ticipates a decline in exports stablizing the GSC and the Ministere des Ressources • China has initiated a major 2 to 3-year pro- around 1.9 million tonnes by the year 2000. Naturelles du Quebec has provided defini- gram to compile its first magnetic database (MJ 3/29/96) tive proof that porphyry mineralization in of the country. The China Aeromagnetic • The Debeers marketing arm appears to the Chibougamau district of northern Que- Mapping Project (CHAMP) will employ have scored again big-time with Holly- bec is not only an integral part of the ore- Canadian, U.S. and British firms. They will wood’s recent Oscar’s extravaganza. De- bearing system responsible for the produc- use the global positioning system to carry Beers was the big sparkler of the night, tive Cu-Au vein deposits, but also is of out high-resolution, aeromagnetic surveys highlighted by the king’s ransom in dia- Archean age. This demonstrates that con- to amass data expected to encourage for- mond jewellery sported by participants trary to conventional wisdom, Archean eign investment in China’s mineral and pe- such as Woopi Goldberg and Goldie Hawn, porphyry deposits can occur, a fact with troleum sectors. (NM 25/03/96) while winning actors, directors and support wide ranging implications for exploration in Shield areas around the globe. • Venezuela is currently preparing a new staff only got to carry off numerous dupli- mining law for that country which is ex- cates of the famous statuette. Retail sales • It is reported that the Columbian govern- pected to be made final by mid-year. The in North America should improve as the ment is going to introduce legislation to new law includes a revised fiscal and regu- public rush to imitate their favourite cellu- regulate the emerald business. Better scru- latory regime for gold mining investment loid heroes! tiny of exports is needed as the emerald in the country, and it is expected that it will • trade has long been used to launder profits include a substantial increase in gross roy- CIDA’s new $2.3 million project to from drugs and the new regulations will strengthen data management in the Zim- alty fees which stand currently at 1%. (NM help prevent people from illegally bringing 1/04/96) babwe Ministry of Mines is paying big money into the country. At the same time dividends for mineral exploration in that the government is concerned with declin- • Diamond-bearing lamproite has been dis- country. Only a few years ago geoscience ing sales, especially to Asia, due to a de- covered in within the Adrianne Pipe at documents were piled high in cabinets and cline in emerald production. Columbian Leek Springs, California by Diadem Re- relatively inaccessible to industry. Now emerald production currently consists of sources. A small, 200 lb., sample contained potential investors and exploration compa- stones of lighter colours and tones while 130 clear diamond shards weighing about nies can get maps, reports, theses, scien- the international market wants deep green 0.75 carats. This discovery at Leek Springs tific articles and other information on CD- colours and medium tones. The only fine is the first time diamond indicators have ROM. The data management project Columbian emerald available today is the been found within an active plate margin involves scanning more than 200 000 rough that was found several years ago setting. (NM 4/15/96) pages of documents and over 20 000 maps coming out of the wreck of the Atocha. (GF and plans which are made available on v13, #4) • Vietnam’s National Assembly recently seven computer work-stations around the passed a new mining law granting overseas country. (NM 11/03/96) • There has been a distinct upswing in the investors the right to exploit non-petro- mining industry over the past year. Four • leum minerals, following relaxation of for- An international conference on mining in- major meetings of exploration and invest- eign ownership laws in February, 1995. vestment held recently in Cape Town was ment professionals have logged record at- (MJ 4/5/96) told that African governments now realize tendance for recent conferences. The the importance of targeted incentives to Northwest Mining Association’s Spokane • After almost a century of base metal min- boost their flagging mining sectors. Sev- meeting logged 3440 registrants, com- ing, operations at the Tsumeb copper-lead- eral speakers admitted mining had been pared to 3098 in 1994; BC’s Cordilleran silver mine in the Otavi Mountainland area badly affected in the past by state interven- Roundup in Vancouver recorded over 2000 of northern Namibia are about to be wound tion and economic mismanagement. New delegates compared with a “normal” year down. Tsumeb, although a significant met- laws and general reforms in the areas of of about 1500; the Prospectors and Devel- als deposit by a number of criteria, is per- foreign investment and mining are starting opers Convention in Toronto had record at- haps most famous for the rare and beautiful to have a positive impact, particularly in tendance, particularly international dele- mineral crystals the mine has supplied to light of a positive attitude to resource de- gates, of about 4700; and, the Society for the world over the years. (MJ 3/29/96) velopment, foreign investment, and in- Mining, Metallurgy & Exploration saw a • creasing political stability. record 4600 registrants at their meeting at Staff of the now disbanded US Bureau of Mines have formed a private company, • the Phoenix Civic Plaza. Much of this ac- The People’s Republic of China is consid- tivity is from developing countries who are Mineral Information & Research Associ- ering revisions to its mining policies. Re- working hard to encourage mineral explo- ates, to pick up where the government left cently a delegation visited several U.S. ration & development. off. The group based out of Spokane, mining operations and met with industry Washington, offers mineral property and government representatives. China has • Brazil’s government is bent on instilling evaluation & environmental studies, pro- been reviewing U.S. mining industry eco- the perception that foreign investment is ject management, and access to GIS and nomic principles, regulatory practices, welcome. Constitutional amendments in database services. (NM 4/1/96).

8 The Gangue No. 52 INDONESIA Philippine ± IndoIn PacificPlate Mineral Deposits SianaSi CooC & Magmatic Arcs PHILIPPINESHILIPPINES MotherlodeM Magmatic Arcs MasaraM Eurasian Plate HijoH N Miwah MALAYSIA Late Miocene & Pliocene WEST Tertiary, Central BRUNEI Sulawesi Kalimantan Arc East Mindanao Early & Mid-Tertiary Arc EAST Late Cretaceous SUMATRA Bintan (Al) MALAYSIA Busang Bulagidun Pacific Plate Kelian Mesel Gebe (Ni) Masupa Mt. Muro Malala Tombulilato Ria (Mo) Gag (Ni) Kelapa KALIMANTAN Kampit (Sn) Lebong Tandai Ampalit Soroako (Ni) Lebong Donok) Pomalaa (Ni) GrasbergGras / Ertsberg IRIAN Lebong Simpang JAYA OK TediPAPUA JakartaGunung INDONESIA Pongkor Lerokis / NEW Cikotok GUINEA JAVA Kali Kuning Jampang Porgera Kerimenge Cikondang Tolukuma BatuB t HijauHij TIMOR Medial Wau Pre-Tertiary Irian Jaya Hidden Valley Sumatra Meratus Arc Arc Sunda-Banda Km Arc Indo-Australian Plate 500 Mi Compiled by Brian Grant, Victoria, BC relationships has also resulted in assimilation and/or burial of older arcs by younger ones. Understanding the complexities of The Indonesian and Philippine archipelagos form part of the Pacific these thick volcanic piles in Indonesia will be key to under- Rim of Fire. They are the result of a complex history of tectonic events standing the mineralization controls for deposits such as Busang. and processes including subduction and arc magmatism near destructive In particular it appears this process of arc overlap has oc- plate boundaries. These processes, and in particular the formation of curred in central Kalimantan and may be a major factor in ex- magmatic arcs and associated gold and base metal deposits, accompany plaining the enhanced concentration of gold in the rocks of this the northward drift of the Indian-Australian Plate, its collision with the area. In its early stages of formation the Sumatra-Meratus Oro- Sundaland continent, and the westward drift of the Pacific Plate. gen, a major arc, curved northeast from central Java then curved The southwest Pacific area is one of the most tectonically complex, to the northwest through Kalimantan. Significant gold occur- active regions of the earth’s crust. Paleotectonic reconstructions indicate rences are known throughout Western Java and Sumatra associ- that recently discovered epithermal gold deposits of the region formed in ated with this pre-Tertiary arc. Then in Tertiary time the Central tectonic settings essentially similar to those which can be observed today. Kalimantan Arc, trending north-south along the length of Ka- The most common setting results from the subduction of an ocean plate limantan and curving to the west, was formed and much of this beneath another ocean plate and this process can be observed in the arc was laid down over the older rocks of the Sumatra-Meratus Solomon Islands, offshore of New Guinea, the Mariana Islands and in a Arc. The area of overlap of these two gold-rich regimes is highly complex fashion in Indonesia and the Philippines. The tectonics of Indo- prospective for world-class, epithermal gold deposits. nesia are complicated by the presence of several micro-fragments of Indonesia’s total gold resource was known to be at least 2650 continental crust, and the change from northward subduction of oceanic tonnes prior to the discovery of Busang. Copper-gold porphyries parts of the Australia-India Plate beneath the Sundaland Craton in Suma- (Grasberg, OK Tedi, Batu Hijau) have been the major source of tra and Java, to southward subduction of the oceanic Pacific Plate beneath gold in Indonesia, accounting for 1650 tonnes of gold. The bal- the Australian Craton to the east, as in West Irian. ance of Indonesia’s resources are contained in a variety of deposit Indonesia and the Philippines contain over 20 000 km2 of fossil and categories including skarn (Ertsberg, Big Gossan, Wabu), epi- active magmatic arcs. The formation of mineral deposits is an inherent thermal/vein/breccia deposits (Busang, Mt. Muro, Kelian, Mesel, part of the arc-building process, and the evolution of all major gold Lebong Donok, Jampang, etc.), sediment-hosted, and exhala- deposits in the region occurs within these arcs, particularly those of Late tive/VMS deposits. The Grasberg/Ertsberg is the single largest Tertiary (Neogene) age. The Tertiary is known around the world as a gold deposit in the world with a combined reserve exceeding 1.13 productive metalliferous period. Destructive plate boundaries have char- billion tonnes at 1.3% Cu and 1.42 g/t Au. The contained gold acteristic high rates of uplift and erosion, particularly in a tropical envi- exceeds 51 million ounces. If one adds the projected resource of ronment such as in Indonesia and the Philippines. As a result, ore deposits 30+ million ounces at Busang, Indonesia is unquestionably a contained in older arcs are more likely to be eroded away, and potential leader in gold producing regions alongside South Africa, Abitibi, deposits contained in younger arcs may not yet be exposed. Tertiary arcs Nevada, and Central Asia. in the Indonesian and Philippine archipelagos are still well preserved, yet Selected References exposed by erosion, and are therefore highly prospective geological tar- gets for exploration. The islands of Indonesia and the Philippines have Carlile, J.C. and Mitchell, A.H.G. (1994): Magmatic Arcs and Associated Gold and over 9000 km2 of Neogene arcs. This is a greater length of prospective Copper Mineralization in Indonesia, Jour. of Geochem. Exploration, v50, pp 91 - 142. Neogene magmatic arcs, on land, than in any other region of the world. Carlile, J.C. (1996): Indonesia and the Philippines: Increased Focus, Supplement to The Indonesian archipelago is the result, not of a simple arc building the Mining Journal, Mining Journal, February 2, 1996. process, but of a highly dynamic system which has resulted in over fifteen Ettlinger,A.(1996):Indonesia,ElephantHuntingintheJungle,WolvertonSecurities, major, and numerous minor volcanic arcs formed due to the prolonged Research Report, 16p. collision and subduction in a complex tectonic environment. As the crus- Marcoux, E. and Milesi, J-P (1994): Epithermal Gold Deposits in West Java, Indonesia: Geology, Age and Crustal Source, Journal of Geochemical Explo- tal plates move over time so do the locations of associated magmatic and ration, v50, pp 393-408. volcanic arcs. As these arcs migrate they leave a thick pile of volcanic White, N.C., Leake, M.J., McCaughey, S.N. and Parris, B.W. (1995): Epithermal rocks which may host economic deposits. In Indonesia this constant Gold Deposits of the Southwest Pacific, Journal of Geochemical Exploration, building and migration of arcs resulting from the complex inter-plate v54, pp 87-136.

May 1996 9 WORLD ATLAS OF URANIUM DEPOSITS First Edition: 1995 1:30 000 000-scale Map

The first atlas of its kind was recently published by the International Atomic Energy Agency (IAEA). It contains information on 582 uranium deposits ATLAS distributed in 48 countries.

Types of deposits, size and production status are indicated by different shapes, sizes and colours of symbols. The legend includes the names of all deposits plotted.

The map at 1:30 000 000-scale was produced by the Geological Survey of Canada under contract to the IAEA. It is available from: International Atomic Energy Agency Sales & Promotion Unit, Division of Publication P.O. Box 100, A-1400 Vienna, Austria 200 Austrian Schillings folded; 250 rolled Northeast Eurasia’s Nickel '96 Magnetic & Tectonic Anomalies Mineral to Market Oklahoma-based Conoco Inc. has sponsored a major inter- Australian Institute of Mining & Metallurgy national geoscience project, managed by the Geological Survey (Kalgoorlie Branch) of Canada - Atlantic. The objective has been to compile a mag- Australian Institute of Geoscientists netic database of one of the largest and more complex geological Western Australian School of Mines Aim: regions in the world. To cover the present status & future developments for nickel and its A multinational team of geoscientists representing Russia, associated cobalt and copper, from exploration through Processing, China, Mongolia, the USA, the UK, and Canada, pooled their to marketing and financing. information and expertise to develop a combined magnetic and Topics: tectonic map of Russia, China, Mongolia and adjacent marine There will be a common plenary technical session, featuring speakers areas. from major nickel companies, followed by parallel technical sessions. This new map, encompassing about 25% of the world’s Session 1: land area and consisting of data not available until the comple- Geology, genesis, Exploration, Geophysics, Geochemistry Mine Evaluation & Modelling of ore deposits (sulphide & laterite) tion of this project, offers an unprecedented illustration of major geological structures and their magnetic expressions in a region Session 2: with a complex crustal history. It provides a broad framework Mineralogy, Mineral Processing, Metallurgy & Marketing, for exploration and resource assessment by illustrating the scope Economics and Finance. of continent-wide processes that affect mineralization. Prepared using the computer facilities of Conoco Inc. and For further information contact: GSC Atlantic, the map features text material in Russian, Chinese Session I Session II and English and is available from the Geological Survey of Mr. Ian Neuss Prof Eric Grimsey Outokumpu Mining Australia WA School of Mines Canada as GSC Open File # 2574. 1st Flr Burswood Court P. O . B o x 5 9 7 141 Burswood Rd., Egan Street As part of an unrelated project, Mongolian geologists have Burswood, WA 6100 Kalgoorlie, WA 6430 also recently published an English-language book on the min- Tel: 09-334-7333 Tel: 090-80-5182 eral resources and geology of their country. This work, entitled FAX: 09-472-3168 FAX: 090-80-5181 Guide to the Geology & Mineral Resources of Mongolia,ex- plores the country’s stratigraphy, magmatism, tectonics and Kalgoorlie, Australia, metallogeny. Information on over 300 deposits is included as Nov 27 - 29, 1996 are numerous maps. Further information on this data is available from PDM Information Technology in Toronto (416-868-9487)

10 The Gangue No. 52 MDD Announces Publication of the: ATLAS OF ALTERATION

Pre-publication price: $40.00 Cdn/US (Until August 1, 1996) Pubication price: MDD members - $45.00 Cdn/US non-members - $55.00 Cdn/US Order from: Geological Association of Canada MDD Dept. of Earth Sciences, Memorial Univ. of Nfld. St. John’s, Newfoundland, Canada A1B 3X5 Alteration Tel: 709-737-4062 FAX: 709-737-2532 E-mail: [email protected] Atlas Atlas of Alteration Expected Publication Date: MDD Alteration Atlas 1996 Spring - Summer 1996 A Field & Petrographic Guide to Hydrothermal Alteration Minerals

The “Atlas of Alteration” will facilitate the recognition of major alteration minerals in both field and laboratory settings. It will provide an introduction to major types of alteration, referenced to the environment of formation and the relationship to ore deposits. The goal of the volume is to cover standard alteration types and textures using colour photographs and consise, short descriptions. The atlas is designed for use by professional geologists and students. This volume is a compendium of 50 contributions by numerous international authors. It contains 50 colour plates, each comprised of either 2 or 4 photographs of alteration mineral textures in outcrop/hand sample and thin-section. Each colour plate is complemented by a facing page of text describing common mineral alteration type, characteristics in outcrop, hand sample and thin section, related and accessory minerals, environments of deposition, example deposits, references and photo captions. The Atlas is published as an 8.5x11”, soft-covered book. Alteration minerals are organized alphabetically by mineral name and formula. A cross-reference table links alteration minerals to deposit types. Charts of standard mineral optical properties are also included. The Atlas of Alteration is a collaborative project between the Mineral Deposits Division - GAC, the Mineral Deposits Research Unit at The University of British Columbia, and PetraScience Consultants Inc. The concept of the atlas was developed in 1993 by Anne and John Thompson who, with Kathryn Dunne, are the volume editors. Anne J.B. Thompson is the President of PetraScience Consultants Inc., John F.H. Thompson is the Director of the MDRU, and Kathryn P.E. Dunne is Series Editor and Publications Chair for the MDD.

MINERAL DEPOSITS DIVISION - GAC Membership Information &Application Regular Member: Associate Member: Corporate Subscription: $10 Cdn/year $20 Cdn/year: $25 Cdn/year: Must be GAC member Non-Residents of Canada Corporate or Library. GAC Membership No. who are not members of GAC. The Gangue subscription only. (see latest mailing label for No.) Name: Address: Country: GAC Member #: Postal Code: E-mail: Tel: FAX: MC/Visa Card #: I enclose a cheque for: Cdn/US $ Expiry Date: Signature: Mail Application to: Geological Association of Canada, c/o Dept. of Earth Sciences, Memorial Univ. of Newfoundland St. John;s, Newfoundand, A1B 3X5. Tel: 709-737-7660; FAX: 709-737-2532; E-mail: [email protected]

May 1996 11 Ranch Lake Kimberlite In The Central Slave Craton: The Mantle Sample

Harrison Cookenboo, Canamera Geological Ltd Ranch Lake Pyropes (n=58) Introduction: 14 12 The Ranch Lake kimberlite intrudes Archean granitoids of the Slave craton (Bowie, 1994), 330 km NE of Yellowknife. Drilling has 10 Fig 2 defined the kimberlite to a maximum depth of 350 m. The pipe-shaped 8 body has a surface area of 12 hectares, entirely covered by a small lake 6

Discovery of the kimberlite occurred with recovery of pyrope and Number 4 Cr-diopside indicator minerals from a more than 70 km long dispersion 2 train in November, 1992. The first successful drilling followed in the 0 spring of 1993. Initial caustic fusion tests for diamonds proved the pipe diamondiferous, and subsequent drilling provided kimberlite for a

601-650

701-750

801-850

901-950 small bulk test. In the largest test for diamonds a combination of crush- 501-550

1101-1150

1001-1050 1201-1250

1301-1350 ing and density separation techniques were used on 28.5 tonnes of 1401-1450 Ranch Lake kimberlite, which yielded a grade of roughly 20 Ct/100t. Ni-in-pyrope temperatures °C In addition to the diamond tests, numerous microprobe analyses formation at temperatures between 950° and 1150°C (Fig. 2) using a were performed on xenocrystic indicator minerals. Some analyzed recent calibration of the Ni-in-pyrope geothermometer developed by grains were collected from the indicator mineral dispersion train down- Griffin et al.(1989). ice of the pipe, others from heavy mineral concentrates of the kimberlite Eclogitic garnets itself. The results of these microprobe analyses are described briefly, with emphasis on aspects of the chemistry relevant to the type of mantle Ninety-seven garnets representing the full spectrum of orange to sampled by the kimberlite. Following the microprobe results is an pink colors present in Ranch Lake heavy mineral concentrate were equally brief summary of the nitrogen defects determined by infrared analyzed by electron microprobe. The selected grains comprise a con- absorbance (IR) spectra from the diamonds, which may help further tinuum of Cr concentrations below 2.3% Cr2O3, with the most pink constrain the mantle below Ranch Lake. shades being the most Cr-rich (Fig. 3). Na2O and TiO2 for the 66 Indicator Mineral Chemistry lowest-Cr grains (Cr2O3 below 0.75%) suggest low-Cr orange garnets include both eclogitic garnets from the diamond stability field and Electron microprobe analyses of purple and orange garnet, Cr- low-Cr megacrysts associated with kimberlite magma (Fig. 4). Eight- diopside, orthopyroxene, and chromite were obtained at The University een of the 66 low-Cr garnets have Na concentrations of 0.10–0.21 wt% of British Columbia. In addition, 58 representative pyropes were ana- Na2O, comparable to eclogitic garnet inclusions in diamond. lyzed by proton microprobe for trace elements including nickel, first at Enstatite the Univ. of Guelph, and then as a check at CSIRO in Australia. Brief descriptions of the microprobe results emphasizing aspects relevant to Fifty-one orthopyroxene (OPX) grains were analyzed by micro- their mantle origin are provided, accompanied by plots of cation or probe, and 75% plot within the field for OPX from diamondiferous oxide abundances where appropriate. lherzolite (ODL field in Fig. 5; after Ramsay and Tompkins, 1994). Following the microprobe results is a brief description of the These OPX have the very low Al contents common to enstatite from IR-spectra from Ranch Lake diamonds, and discussion of the spectra’s diamond inclusions which is significant because Al in OPX is strongly implications to the thermal exposure of mantle sampled by the kimber- dependent on pressure, and is the basis of several geobarometers (lower lite. A12O3 contents occur at higher presssures). An interesting approxi- mate application of one of these geobarometers (Perkins and Newton, Pyropes 1980) to Ranch Lake enstatite analyses is possible by graphical ex- More than 2000 pyropes representing all shades of purple-tinted trapolation of their experimental conditions. Using such an extrapola- garnets have been collected from Ranch Lake core and the down-ice tion, and assuming geologically reasonable crystallization tempera- dispersion train for analysis by microprobe. These grains are Cr-py- tures between 800° and 1100°C (similar to temperatures suggested by ropes that plot mostly within the lherzolite trend (Sobolev, 1974; Fig. Orange garnets from Ranch Lake 1), but also include numerous Ca-poor (G10) garnets that plot to the 12 left of Gurney’s 85% line, and Ca-rich garnets including a distinct trend (n=97) of Ca enrichment at constant Cr2O3 concentrations between 4.5 and 10 Fig 3 5.5% (wt % oxide). Roughly 4.9% of the Cr-pyropes (n= 2168) are very 8 subcalcic Cr-pyropes with <4.0% CaO and >4.0% Cr2O3. Similar pro- portions of Ca-poor pyropes occur in some diamondiferous pipes on 23 6 the Kaapvaal craton (e.g., Finsch, Bobbejaan, Kimberley, Jagersfon- Cr O 4 tein, Kaalvellei and Premier, as reported in Schulze, 1994). More than 2 60% of the 58 pyropes analyzed by proton microprobe for trace ele- ments have Ni concentrations between 38 and 70 ppm, which implies 0 01234567891011121314 CaO (wt % oxide) Low-Cr orange garnets from Ranch Lake 1.40 1.20 1.00 0.80 0.60 0.40 0.20 Fig 4 0.00 0.00 0.05 0.10 0.15 0.20 0.25 0.30

12 The Gangue No. 52 Ranch Lake, assuming that N defect aggregation is controlled by Ar- rhenius-type kinetic reactions as theory predicts (Evans and Qi, 1982; Taylor et al.. 1991). Although no unique age or temperature solution is possible because the thermal exposure is controlled by both time and Fig 5 temperature, some relative differences in mantle residence can be in- ferred. For Ranch Lake, the N-rich and A-defect dominant population of diamond and bort must have resided in the mantle at relatively low temperatures (probably 1050°C or lower) for a relatively short period of time. The low thermal exposure for these diamonds and bort suggest origination from a mantle position near the graphite/diamond stability field boundary. In contrast, the B-defect dominant population experi- enced greater thermal exposure and thus probably resided in warmer and possibly older mantle, keeping in mind that the effects of tempera- ture are relatively more important than time (Taylor et al., 1991). most of the Ni-in-pyrope data) it appears that the grains with 0.50% Mantle source: Al2O3 formed at pressures >35 Kb, and those grains with less than 0.35% Al2O3 formed at >40 Kb. Such pressures are within the diamond The xenocrystic indicator minerals from Ranch Lake include stability field at temperatures as low as 800°C (Jacques et al., 1990). compositions similar to inclusions in diamond, and thus imply the Chromite kimberlite sampled the diamond stability field. Furthermore, the vari- ety of different minerals with diamond inclusion compositions suggest Fifty-seven chromites from Ranch Lake core have been analyzed that the kimberlite sampled at least 2 types of potentially diamondifer- by electron microprobe. All are Cr-rich (maximum 68.0% Cr2O3) and ous mantle. That the kimberlite sampled peridotite from the diamond Al-poor, and include 5 grains with compositions similar to chromite stability field is suggested by the microprobe analyses of Cr-pyrope, inclusions in diamond (Fig. 6). Nineteen of the most Cr-rich and Al- OPX, and chromite that are comparable to inclusions in diamond. poor chromites from Ranch Lake have slightly lower Mg contents than Similarly, eclogite from the diamond stability field is suggested by the diamond inclusions, similar to chromites intergrown with diamond in orange garnets with elevated Na O and low TiO . the ‘Mir’ pipe (Sobolev, 1977). 2 2 The most obvious confirmation that the Ranch Lake kimberlite Diamond sampled diamondiferous mantle is the occurrence of diamonds within Infrared spectra have been collected for all 113 diamonds recov- the pipe. Interestingly, the IR spectra from the diamonds themselves ered from the Ranch Lake semi-bulk test. These spectra include absor- support the suggestion, based on the peridotitic and eclogitic indicator bance peaks intrinsic to (and characteristic of) the normal diamond mineral compositions, that 2 different mantle sources contributed to crystal structure, as well as peaks attributable to various types of nitro- the kimbertite. From the diamond IR spectra, it is clear that one of the gen (N) defects. The amplitude of the N-defect peaks (relative to the mantle sources has a lower thermal exposure than the other. It is intrinsic diamond peaks) depend on the N concentration, and the posi- tempting to correlate the lower thermal exposure diamond source to tion of the peaks depends on the structure of the defect. Three types of eclogitic mantle, constructing a speculative scenario of relatively N defects termed the A, B, and D, account for most absorbance in IR -1 young (perhaps recently subducted) lithosphere contributing the N-rich spectra between 1150 and 1300 cm (Taylor et al, 1991). Experiments and A-defect dominant diamonds, while ancient peridotitic mantle and theory (Davies, 1981; Taylor et al., 1991) suggest that the A-de- from the lithosphere keel contributed the B-defect dominant stones. fects, consisting of two adjacent N atoms (Davies, 1976), anneal into However, tests including stable isotope and inclusion studies in dia- B-defects, comprising 4 tetrahedral N atoms (and possibly D-defects; monds are needed to support such a speculative correlation. Clark and Davey, 1983), at a rate dependent on their thermal exposure Acknowledgments (thermal exposure = combined effect of time & temperature during mantle residence). Thus the relative proportion of A-defects compared Collection and preparation of samples used in this study is a group to B-defects constrain the thermal history of diamonds, with A-defect effort of both past and present employees at Canamera Geological Ltd, dominant diamonds constrained to relatively low themal exposure, and and I am truly grateful for their efforts. I especially want to thank John B-defect dominant diamonds constrained to higher temperatures, and Dupuis, Bill Dynes, and Lytton Minerals for involving me in this probably longer mantle residence times. project, and permitting me to publish this data. I also thank Jennifer The percent A to B defects has been calculated for Ranch Lake Pell of DIAND for sharing many insights into kimberlite geology in diamonds by comparing their IR spectra to synthetic spectra of varying the Slave. Errors and interpertations made despite the best help of A to B defect ratios (Woods, 1986). The D-defect has been disregarded theabove listed groups and individuals, however, are the responsibilty for this qualitative exercise. Most of the Ranch Lake diamonds with of the author. detectable N defects fit within 2 distinct populations (Fig. 7). The first References population has 95 to 100% A-defects and thus are nearly pure type 1aA Bowie, C., (1994): Cartographic overlay of Geology, Slave craton and environs (OF 2559) diamonds, typically N-rich, with N concentrations between approxi- on shaded total field magnetic data, District of Mackenzie, Northwest Territories; mately 500 and 2000 ppm of IR-active nitrogen. Included in this popu- Geological Survey of Canada, Open File 2964, Scale 1:1 000 000. lation are all the bort and cubic diamonds, but also many of the largest Clark, C.D. and Davey, S .T., (1983): One-phonon infrared absorption in diamond; Journal and clearest stones. The second population is strongly B-defect domi- of Physics, C, v 17, p. 1127-1140. nant (type 1aB), with IR-active nitrogen concentrations <400 ppm. Davies G., (1981): Decomposing the IR absorption spectra of diamonds; Nature, v 2907 p. 40-41. At least 2 distinct thermal histories are required to account for the Davies, G., (1976): The A nitrogen aggregate in diamond - its symmetry and possible contrasting A-defect and B-defect dominant diamond populations at structure; Journal of Physics, C: Solid State Physics, v. 9, L537-L542. Fig 7 O

Cr

Fig 6

MgO

May 1996 13 Mobile Metal Ions A New Mineral Exploration Tool

by A.W. Mann, R.D. Birrell, L.M. Gay, A.T. Mann, J.L. Perdrix & K.R. Gardner Geochemistry Research Centre, W Australia and Wamtech Pty., Ltd., W Australia

Partial extractions have a long history in geochemistry. Their use probably reached an hiatus in the 1970s when the transition to full sample digestion with rapid turn-around through large laboratories became the stand- ard method for exploration analysis. At that time, detection limits stood at the low ppm level for most elements. Since then, the lower detection limits for most elements, particu- larly those of economic interest, have de- creased by three orders of magnitude, to the ppb level. This almost imperceptible ‘revolu- tion by stealth’, while readily welcomed by most explorationists, has not been fully ex- ploited. In addition to being able to carry out ‘routine’ geochemistry at lower levels, the new instrumentation has opened up new ave- and careful use of weak extractants and very • field inspection, program design and sam- nues in the methods of selecting sample ma- low level chemical pre-concentration and pling; terial for analysis which will maximize the analysis techniques can be used to obtain sig- • digestion and extraction of metals; opportunity for detection of ore bodies. Partial nificant and reliable element signals to enable • the anomaly patterns to be enhanced, re- analysis and QC (Cu, Pb, Zn, Ni, Cd, Au, extraction is one technique which has, and Ag, Pt & Pd); and, will continue to benefit from this revolution. solved, and interpreted for the detection of blind ore-bodies. While the exact mechanisms • interpretation, recommendations and re- The aim of a partial digestion is to release for release, transport, and ‘fixation’ of the port. some of the metal contained in a soil to solu- metals are, in our case, the subject of spon- A number of separate digestions is re- tion. Mobile metal ions are those which are sored research and confidential, the technique quired, because no one digestant is capable of released to solution from the use of very weak is of considerable importance to the explora- extractants - extractants which deliberately do tion industry, because of its apparent ability to providing optimum extraction of all nine met- not attack the substrate or matrix. A large per- operate in deeply-weathered terrain, and in als. Digestants, details of which must remain centage of mobile metal ions appears to be some cases through considerable thicknesses proprietary, have been screened and selected derived from metal-containing ore-bodies, of overburden. Some 7000 samples, involving for their ability to extract only the very over 50 000 analyses have now been subjected weakly-attached (mobile) metals. Extractants Evans, T., and Qi Z., (1982): The kinetics of theaggregation of nitrogen atoms in diamond; . Proceedings, Royal to the Mobile Metal Ion Process. used are multi-componet mixtures of water Society of London, A, v 381, p. 159-178. The Mobile Metal Ion Process (MMI)® soluble organic and inorganic chemicals. Fol- Griffin, W.L., Cousens, D.R., Ryan, C.G., Sie, S.H. and lowing digestion and analysis, ‘background’ Suter, G.F., (1989): Ni in chrome pyrope; a new for each element is calculated to provide a geothermometer; Contributions to Mineralogy and The following are the major steps in the ‘Response Ratio’ at each sample point for Petrology, V. 103, p 199-202. process: Jacques, A.L., Haggerty, S. E., Lucas, H. and Boxer, G. L., each element. All subsequent interpretation of (1989): Mineralogy and petrology of the Argyle • evaluation of background information, in- data is based upon application of the appropri- (AK1) lamproite pipe, Western Australia. in J.L. Ross cluding existing geochemical data; ate thresholds to the Response Ratios. (ed.) Kimberlites and related rocks, volume 1, Fourth Internatn’l Kimberlite Conf., Perth , 1986, p. 153169. MMI Response Ratios Over a Base Metals Deposit at 700 m Depth Perkins, D. And Newton, R.C. (1980): The compositions of coexisting pyroxenes and garnet in the system Ca0-MgO-Al2O3-Si2O at 900-1100°C and high Zn/250 pressure. Contributions to Mineralogy and Petrology, Pd v75, p 291-300. Cd Schulze, D.J. (1994): abundance and distribution of low-Ca garnet harzburgites in the subcratonic lithosphere of Pb southern Africa; in, Kimberlites, Related Rocks and Cu Mantle Xenoliths, p 327-335. Sobolev, N.V., (1977): Deep seated inclusions in kimber- lites and the problem of the composition of the upper mantle; American Geophysical Union, 279 p. Taylor, W.R., Jaques, A.L. and Ridd, M., (1990): Nitrogen- defect aggregation characteristics of some Australian diamonds, Time-temperature constraints on the Response Ratio source regions of pipe and alluvial diamonds; Ameri- can Mineralogist, v. 75, p. 1290-13 10. Woods, G.S., (1986): Platetets and the infrared absorption of type la diamonds; Proceedings of the Royal Society of London, A, v 407, p. 219-238. 900W 650W 500W 375W 150W

14 The Gangue No. 52 et al., 1993). The CHIM method (clearly very similar to the MMI technique, even to the use of carbon electrodes for pre-concentration) and Gas Vapour Phase method (Magellan, 1993) are other methods of accessing metal ions from soils which differ from traditional partial extraction techniques. The traditional methods have, in many cases, used special extractants to perform selective extraction-re- lease of metals from specific substrates. These methods need to ensure that the extractant Case History Results may represent anomalies which are associated does not dissolve an exessive amount of the with a possible structural repeat of minerali- substrate and release metal which contributes Over 70 case history and working studies zation. have been carried out using the MMI process to ‘background noise’. in four continents. Table 1 gives an indication Discussion 3) Possible mechanisms of formation of MMI anomalies of the range of situations covered, and the 1) Summary of essential features of relative success achieved. MMI anomalies: The Geochemical Research Centre Two of these examples are examined • MMI anomalies exist, and can be used to (GRC) at Technology Park, Bentley, W. Aus- here in detail. Figure 1 shows the MMI anom- detect buried mineralization; tralia, operates a research program with the aim of providing participants with informa- aly on a transect across strike of buried base • MMI anomalies are clearly different to metals mineralization. tion on the mechanism of formation of mobile conventional geochemical anomalies in metal ion anomalies. The Centre is currently In the above example, note that the zone their appearance, intensity and potential considering mechanisms involving vapour of mineralization at a depth of 700 m, projects application to exploration; (aerosol) transport and chemical release of to surface at very closely the position of the • The mechanism of formation of MMI metals during weathering. The elucidation of very sharp, multi-element MMI anomaly ( the anomalies is almost certainly very differ- the mechanism isnot just concerned withthe Response Ratio for Zn has been divided by ent from that responsible for the forma- mode of transport, but also with the form of 250 to appear on the same scale). tion of normal multi-element fixation of the metals in the soil regime. For The second example, is from Nepean geochemical anomalies; this, the Centre is utilizing study areas pro- nickel deposit near Coolgardie, Western Aus- • Not all elements behave in exactly the vided by participating companies to examine tralia. The ore zone contains massive nickel same manner; and the effects of different regolith, mineralogical, sulphide, with sulphides of copper, lead, co- • MMI anomalies are sometimes climatic and geomorphological situations on balt and minor gold, platinum and palladium ‘swamped’ in areas of recent, rapid the presence, strength and persistence of mineraliztion. Several factors are of interest transport. anomalies. in this particular study. First, the nodular fer- Some of the individual and relevant ob- Conclusions ruginous material to the west of the mineral- servations which lead us to these conclusions ized zone, which shows high nickel responses are: Due to the increasing need for explora- by conventional analytical procedures, does • tion techniques to operate effectively in areas MMI anomalies comprise only elements of deeply weathered or transported overbur- not have a high MMI response. This is shown present in the mineralization in signifi- in Table 2. den, this new geochemical technique has the cant amounts; potential to complement geophysical methods This table highlights that two different • Anomalies are sharp, and in most cases for the detection of blind mineralization. Be- MMI thresholds are appropriate in the case of directly overlay and define the extent of cause of the very sharp and coincident nature nickel, one which distinguishes ultramafic the surface projection of buried primary of the anomaly peak, it has the potential to rocks from rocks with lower Ni contents (e.g., mineralized zones; significantly reduce drilling costs. As such the mafics), and the second to distinguish poten- • When primary mineralization is high exploration budget will be affected by the in- tiall-mineralized areas within ultramafic se- grade, MMI anomalies are capable of troduction of the technique into the explora- quences, from ‘barren’ ultramafic. The MMI penetrating significant thicknesses of tion program, in some cases by reductions of response over Ni mineralization is, in this overburden; and, up to 30 - 50%. Any partial digestion process case, 75 times background, while the MMI • is dependent on the correct, systematic and response over barren ultramafic is 6-times The incidence of false anomalies is very low compared to normal geochemical careful execution of a number of steps, that background. The data in Table 2 also show methods. these methods cannot be easily translated to a that in this case conventional geochemistry rapid/routine analytical technique. As such, fails to provide a distinction between the Ni 2) Relationship of MMI to other par- tial extraction geochemical methods: partial extractions will remain relatively ex- content of the ferruginized soil over barren pensive compared to routine analysis, and ultramafic, and the Ni content in soil over One of the first reports of the ‘geogas’ they must be implemented into exploration mineralization, whereas the MMI partial ex- phenomenon was by Malmquvist & Kristians- programs with due diligence and care. An- traction clearly does. son (1984). In this report the primary gases other word of caution is also required; there is At Nepean, the MMI response for Ni is detected were nitrogen, argon, oxygen, and often a tendency, after the initial scepticism at a maximum over the ore zones, and deline- methane over a massive sulphide deposit in has abated, to regard any new geochemical ates several ore zones with remarkable accu- Central Sweden. Subsequent variations of the technique as a universal panacea, and in some racy. As noted in the case of other base metals, technique utilized plastic collection strips and cases to misapply it. The MMI technique will there is the coincidence of several anomalies very sophisticated instrumentation to detect be no different. There is a practical limit to its from individual elements contained in the ultra-trace levels of metal ions on the collec- usefulness, which is dependant upon future mineralization, principally Pd and Cu. In tors. Compared to other techniques, sample developments in analytical techniques and ex- many cases, there is an associated, but later- collection is not as robust, and the technique tractants. However, if carefully applied in an ally-displaced, weak Au-Ag anomaly over the is very expensive when applied on the scale integrated and systematic manner, it seems basal contact of the ultramafic unit with mafic required for exploration. certain to make a large contribution to the units in the sequence. Several other pre- The CHIM, MPF and TMGM methods detection of buried mineralization. viously-undetected, prospective zones are in- developed in the USSR (Antropove et al., Acknowledgments dicated by MMI Ni Response Ratios to the 1992) during the 1980s recently came under east of the mined zone, and to the east of a increasing scrutiny. The USGS recently pu- The work described in this paper in- postulated fold axis (Kirkpatrick, 1985). They bished their findings on this technique (Smith cludes any carried out under the auspices of

May 1996 15 the GRC. Acknowledgments are due to those companies which have kindly permitted us to release the broad outlines of the case history surveys, and to those companies and MERIWA who have committed to long term research. Geoscientists in Ontario are trying (once again) to achieve professional registration. References This time, the chance of success appears to be significantly greater. Antropova, L.V., Goldberg, I.S., Voroshilov, N.A., Ryss, As of March 10, 1996, the Association of Geoscientists of Ontario was formed, Ju.S. (1992): New methods of regional exploration for following from the Committee for Professional Registration of Geoscientists in Ontario. blind mineralization: application in the USSR, J. Geo- The aim of this new organization is to promote geoscientist registration in Ontario, and to chem Explor., v43, p 157-166. provide communications with geoscientists as the registration process develops. The in- Clark, J.R. (1993): Enzyme leaching of soils developed on augural meeting, held to coincide with the PDAC, was attended by some 60 geoscientists. transported overburden enhances anomalies near bur- By the end of March 1996, over 300 geoscientists across Ontario have joined. The aim is ied mineral deposits, SEG conference. Unpublished to have all Ontario geoscientists represented by the end of 1996. report. Kirkpatrick, B.L., (1985): Geological evaluation of Ni The Association is now participating in a combined Task Force with the Professional mine’s potential for further Ni resources, Metals Ex- Engineers in Ontario (PEO) to develop a licensure model for geoscientists within the PEO ploration Report, No. 808. through an amendment to the Professional Engineers Act of Ontario. The intent is to Magellan Petroleum Australia Ltd. (1993): An introduction develop a mechanism similar to those in BC, Alberta, Newfoundland and the NWT. The to gas vapour geochemistry (GVP), unpublished re- geoscientists on the Task Force committee are Bill Pearson, Andy Cooper, and John port. Bowlby, and both parties anticipate presenting a revised Act, incorporating geoscientists, Malmqvist, L. & Kristiansson, K. (1984): Experimental evidence for an ascending microflow of geogas in the to the Legislature in late 1996. ground, Earth & Planetary Science Letters, v70, p The Association is intended as an interim organization with the principal objectives 407-416. of: identify individual geoscientists in Ontario; facilitate discussion of the registration Smith, D.B., Hoover, D.B. & Sanzolone, R.F. (1993): system; provide a formal organization to support the jointly prepared Association of Preliminary studies of the CHIM electrogeochemical method at the Kokomo Mine, Russell Gulch, Colo- Geoscientists of Ontario / PEO submission to the Ontario government; and, provide a rado, J. Geochem Explor., v46, p 257-278. financial resource for this phase of the process. Note: Following the March meeting a Board of Directors was elected, and an executive formed. The Board is comprised of Bill Pearson (President), John Bowlby (Vice-Presi- Further information on this technique dent), Janet Haynes (Secretary-Treasurer), Linda Bloom, Andy Cooper, Mike Cosec, Brian can be acquired from Linda Bloom of X-RAL MacKay, Bob Leech, Gary Pringle and Bill Steibel. Committees have been struck to Laboratories in Toronto, Ontario. Tel: 416- develop the Association’s membership, disseminate information, and to assist the task 445-5755; FAX: 416-445-4152. group discussions. Membership in the Association is open to all geoscientists in Ontario. X-RAL offers MMI analysis under li- Annual membership fee is $25. A non-voting membership is available to full-time students cense from Wamtech Pty. Ltd., West Perth, at a reduced rate of $10. We also welcome corporate sponsors and members. West Australia. For additional information contact: Janet Haynes, Sec-Treasurer, AGO, c/o Char- lesworth & Associates, Suite 101, 77 Mowat Ave., Toronto, M6K 3E3, FAX 416-536- 7724; or, Mark Waychinson, Membership Committee, Mineral Exploration Geologist, Tel/FAX 905-847-6918; e-mail: [email protected] Bolivia’s Mineral Potential

Courtesy of the National Secretary of Mining, La Paz, Bolivia. The Sub-Andean Zone is underlain by gently folded sedimentary rocks of Devonian, Carboniferous, Cretaceous and Tertiary sedimentary Bolivia has a variety of geological environments with a high den- rocks. It is here that the most productive gas and oil deposits of Bolivia sity of mineral deposits and occurrences. are located. The Western Cordillera, which consists mainly of Tertiary and In eastern Bolivia there are extensive outcrops of the Brazilian Quaternary volcanic complexes, consititutes a favourable environment Pre-Cambrian shield, with geological and mineral environments for bulk-mineable, volcanic-hosted precious metal deposits and there similiar to those currently under exploitation in Brazil. These include has been several discoveries in recent years. gold-bearing greenstone belts, layered ultramafic complex with nickel, chromium and platinum-group mineral occurrences, tin & gold alluvi- In the Altiplano, an intermontane basin underlain mostly by Terti- als, precious and sem-precious stones, sediment-hosted Pb-Zn, in addi- ary clastic sediments, volcanic complexes and domes, there are good tion to large iron and manganese deposits. Apart from gold exploration indications of sediment and volcanic-hosted gold and silver epithermal in the greenstone San Ramon belt the Bolivian Pre-Cambrian shield is deposits, similar to those in other precious-metal deposits in northern virtually unexplored. Chile and Nevada. There are also several salt lakes, such as the Salar de Uyuni, the world’s largest salt deposit, which contains high potassium, In northern Bolivia, the Beni and Madre de Dios rivers, which drain lithium, boron and manganese salts and other evaporitic minerals. In from the Andes into the Amazon basin, are considered to have enormous addition, there is a wide variety of non-metallic minerals. potential for alluvial gold and tin deposits. The Eastern Cordillera, made up of folded Paleozoic sedimentary Western Bolivia is the site of some of the most important metallo- rocks, locally overlain by Cretaceous and Tertiary red beds and volcanic genic provinces of the Central Andes. Of particular interest is precious rocks, is known throughout the world as the Bolivian Tin Province metal mineralization associated with Miocene magmatism and volcan- Tin-polymetallic mineralization is associated with batholiths of Middle ism. Tertiary, precious metal deposits have been grouped into four types: Jurassic age and with Tertiary, high-level stocks and volcanic domes. volcanic-dome, porphyry-system, sediment-hosted, and carbonate- hosted deposits. There are bonanza-type deposits of tin, tungsten, bismuth, lead, zinc, silver, gold and antimony. The silver-tin deposits have been world- Traditionally, mining in Bolivia has been labour intensive, due to famous since the 16th century. The most important is the Cerro Rico the exploitation of high-grade, bonanza-type veins. Since 1980, how- deposit in Potosi, which has produced more than 60 000 tonnes of silver. ever, new technology has been introduced to the local mining scene and Recent studies indicate that the Cerro Rico deposit may now contain as there are currently successful heap-leach Au and Ag operations at La much silver as has already been produced. Joya, Toldos and Cerro Rico.

16 The Gangue No. 52 GeoScientists - Wired in the 90s!

This is a Mineral Deposits Division listing for Brown, Glenn, A/Director ODP, Toronto Hitch, Michael, Vancouver Division members and others who have an [email protected] [email protected] interest in economic geology. Buck, Harvey, Winnipeg Hopkins, Janet Vancouver [email protected] [email protected] Names will only be added to this directory by Campbell, Finley, Univ. Calgary Hornal, Robert, Vancouver BC sending an E-mail message containing your: [email protected] [email protected] full name, organization, city/country, are Chandler, Fred C., GSC, Ottawa James, Don, St. John’s NF you a GAC/MDD member? to Brian Grant [email protected] [email protected] at [email protected]. Cheel, Rick, St.Catherines ON Jebrak, Michel, U. Quebec, Montreal [email protected], [email protected] Organizations: Clark, Jim, Montreal PQ Johnson, Elizabeth, Vancouver [email protected] [email protected] MDD: The Gangue Johnston, Stephen, Whitehorse [email protected] Clemson, Beth [email protected] [email protected] GAC Headquarters: Newfoundland Jones, Murray, Vancouver [email protected] Collins, Arlene, Victoria BC [email protected] [email protected] GSC: Canadian Geoscience Info. Centre Joudrie, M. Colin, Santiago, Chile [email protected] Coopersmith, Howard G., Fort Collins, CO [email protected] [email protected] Canadian Assoc of Mining Equip & Services Dalrymple, Bob, Queens Univ. Kiel, Mike, GSC, Ottawa for Export [email protected] [email protected], [email protected] Daughtry, Ken Kissin, Stephen Lakehead Univ. Mineral Deposit Research Unit, Univ. BC [email protected] [email protected] [email protected] Davenport, Peter, St John’s Knox, Alex, Calgary ODP Secretariat [email protected] [email protected] [email protected] Dawson, Ken, North Vancouver Koehler, George, Spokane Steve Scott / Glenn Brown [email protected] Individuals [email protected] Day, Robin Edmonton Kretschmar, Ulrich, Washago, ON [email protected] Abbott, Grant, Whitehorse YK [email protected] [email protected] Debicki, Ruth, Sudbury ON Kyle, J. Richard, U. Texas, Austin, Texas [email protected] [email protected] Alldrick, Dani Victoria BC Laznicka, Peter Winnipeg [email protected] Downes, Michael J., Toronto [email protected] [email protected] Allen, Iain Toronto ON Lefebure, Dave, Victoria [email protected], Dube, Benoit, Ottawa [email protected] Ames, Doreen E., Ottawa ON benoit=dube%cgq%gsc=que- [email protected] Lentz, Dave New Brunswick [email protected] [email protected] Anderson, R. (Bob) G., Vancouver BC Dunne, Kathryn P., Gabriola Is. BC [email protected] Lhotka, Paul [email protected] [email protected] Easton, Mike, Sudbury, ON Ansdell, Kevin, Univ. Saskatchewan Longstaffe, Fred, London, ON [email protected] [email protected] [email protected] Appleyard, Ted, Waterloo ON Ettlinger, Art Montana Macdonald, James, Santiago, Chile [email protected] [email protected] [email protected], Barnes, Chris R., SEOS, Univ. Victoria Frith, Tony, Ottawa, ON MacIntyre, Don, Victoria [email protected] [email protected] [email protected] Barrett, Tim , Vancouver BC Fulton, R.J., Ottawa MacLeod, John L., Calgary, AB [email protected] [email protected] [email protected] Beauchamp, Daniel, Calgary AB Furneaux, Barry T. Qualicum Beach, BC Madeisky, Hans E., Vancouver [email protected], [email protected] [email protected] Beaudoin, Georges, Univ Laval PQ Fyon, Andy, Sudbury Malo, Michel, Sainte-Foy PQ [email protected] [email protected] [email protected] Bedard, Paul, Chicoutimi PQ Giovanni, Di Prisco, Toronto Mann, Dick Bathurst NB [email protected] [email protected] [email protected] Bell, Bob Gordon, Terence M. Univ. Calgary Marchand, Michael, Calgary [email protected] [email protected] [email protected] Bernier, Louis Graham, David, Longuiel PQ McArthur, Gib, Victoria BC [email protected] [email protected] [email protected] Bloom, Lynda, Toronto ON Grant, Brian, Victoria BC Meade, Harlan Vancouver BC [email protected] [email protected] [email protected] Bonham-Carter, Graeme, F., Ottawa ON Grunsky, Eric, Victoria BC Meinert, Lawrence, D., Wash. State Univ [email protected] [email protected] [email protected] Boon, Jan, Edmonton AB Guha, Jayanta, Univ. Quebec Metcalfe, Paul, Vancouver [email protected] [email protected] [email protected] Boronowski, Alex Hart, Craig J.R., Whitehorse YK Meyers, Rick, Kamloops [email protected] [email protected] [email protected] Bottomer, Lindsay, Vancouver Hayes, John P., St. Johns, NF Middleton, Gerard, Hamilton ON [email protected] [email protected] [email protected] Boyd, Trevor, Univ. Toronto Hattori, Keiko Woods Hole Ocean. Inst. Morgan, Alan, Univ. of Waterloo [email protected] [email protected] [email protected], Brown, Derek, Victoria BC Healing, Dave, Castlegar,BC Muttes, Michael E., Brampton ON [email protected] [email protected] [email protected]

May 1996 17 Naldrett, A.J.(Tony), Univ. of Toronto Savard, Martine M., GSC, Ste-Foy Valls, Richard A, Montreal. [email protected] [email protected] [email protected] Nowlan, Godfrey, Calgary Schrijver, Kees, GSC Ottawa van Everdingen, Robert O., Calgary [email protected] [email protected] [email protected] O’Reilly, George A., Halifax NS Schulz-Rojahn, Jorg, Adelaide Australia Waddington, Dennis H, Toronto [email protected] [email protected] [email protected] Palma, Vince Scott, Steven D, U of Toronto Walker, Rick [email protected] [email protected] [email protected] Panteleyev, Andre, Victoria Setterfield, Tom, Ottawa Ward, Mary-Claire, Toronto [email protected] [email protected] [email protected] Pat, Judith, Montreal Sheehan, Peter Watkins, John J. [email protected] [email protected] [email protected] Paul Metcalfe, Vancouver Simpson, Ron, Vancouver Watson, Ken, Timmins [email protected] [email protected] [email protected] Pell, Jennifer, Yellowknife, NWT Singhroy, Vern, Ottawa Werniuk, M. Jane, Toronto ON [email protected] [email protected] 102035,[email protected] Peter, Jan M., GSC, Ottawa Skinner, Brian, J., Yale Univ. White, Mike [email protected] [email protected] [email protected] Petersen-Johns, Daphne London ON Smith, Michael D., Toronto M.V.W. White & Assoc. [email protected] [email protected] http://tnt.vianet.on.ca/comm/tdc Preto, Vic, Victoria BC Spark, Robert, Fredricton Whiting, Ben, Kingston ON [email protected] [email protected] [email protected] Ramshaw, R. Spencer Stewart, Bob, Sudbury ON Williams-Jones, A.E. (Willy), Montreal [email protected] [email protected] [email protected] Ray, Gerry Victoria BC Stott, Greg, Sudbury ON Wilson, Graham C., Toronto [email protected] [email protected] [email protected] Roberts, Gwilym, U. Waterloo Swinden, Scott, Halifax NS Wilton, Derek, St. Johns, NF [email protected] [email protected] [email protected] Rockingham, Chris, Vancouver Tauchid, Mohamad, Nepean, ON Wynne P. Jane, Victoria BC [email protected] [email protected] [email protected] Russell, P. Dawn, Santiago, Chile Thorkelson, Derek, Vancouver Zierenberg, Robert A., USGS/U.Calif-Davis [email protected] [email protected] [email protected] Samson, Iain, Windsor Thurlow, Geoff Corner Brook NF Zolnai, Andrew, Calgary AB [email protected] [email protected] [email protected] Sangster, Al, Ottawa Trudu, Alfonso, Melbourne, Australia [email protected] [email protected] Sangster, D.F., Ottawa Tucker, Terry, Vancouver [email protected] [email protected] Geoscience Hotspots on the Internet Rating Name URL Comments

18 The Gangue No. 52 May 1996 19