oncontextmenu="return false" onkeydown="return false

BESSHI MASSIVE SULPHIDE Zn-Cu-Pb / G04

Cortesia del Gobierno de BRITISH COLUMBIA. Ministerio de Enegia y Minas

IDENTIFICATION

SYNONYM:

Sediment-hosted Ni-Mo-PGE, Stratiform Ni-Zn-PGE.

COMMODITIES (BYPRODUCTS):

Ni, Mo, ( Zn, Pt, Pd, Au).

EXAMPLES

(British Columbia - Canada/International): Nick (Yukon, Canada); mining camps of Tianeshan, Xintuguo, Tuansabao and Jinzhuwoin and Zunyi Mo deposits, Dayong-Cili District (China).

GEOLOGICAL CHARACTERISTICSregrese arriba
CAPSULE DESCRIPTION:

Thin layers of pyrite, vaesite (NiS2), jordisite (amorphous MoS2) and sphalerite in black shale sub-basins with associated phosphatic chert and carbonate rocks.

TECTONIC SETTINGS:

Continental platform sedimentary sequences and possibly successor basins. All known deposits associated with orogenic belts, however, strongly anomalous shales overlying the North American craton may point to as yet undiscovered deposits over the stable craton.

DEPOSITIONAL ENVIRONMENT / GEOLOGICAL SETTING:

Anoxic basins within clastic sedimentary (flysch) sequences containing black shales.

AGE OF MINERALIZATION:

Post Archean. Known deposits are Early Cambrian and Devonian, however, there is potential for deposits of other ages.

HOST / ASSOCIATED ROCK TYPES:

Black shale is the host; associated limestones, dolomitic limestones, calcareous shale, cherts, siliceous shale, siliceous dolomite, muddy siltstone and tuffs. Commonly associated with phosphate horizons. In the Yukon at base of a 10 to 20 m thick phosphatic shale bed and in China the Ni-Mo beds are in black shales associated with phosphorite.

DEPOSIT FORM:

Thin beds (0 to 15 cm thick, locally up to 30 cm) covering areas up to at least 100 ha and found as clusters and zones extending for tens of kilometres.

TEXTURES/STRUCTURE:

Semimassive to massive sulphides as nodules, spheroids, framboids and streaks or segregations in a fine-grained matrix of sulphides, organic matter and nodular phosphorite or phosphatic carbonaceous chert. Mineralization can be rhythmically laminated; often has thin discontinuous laminae. Brecciated clasts and spheroids of pyrite, organic matter and phosphorite. In China nodular textures (~ 1 mm diameter) grade to coatings of sulphides on tiny 1-10 mm spherules of organic matter. Fragments and local folding reflect soft sediment deformation. Abundant plant fossils in Nick mineralization and abundant fossils of microorganisms (cyanobacteria) in the Chinese ores.

ORE MINERALOGY (Principal and subordinate):

Pyrite, vaesite (NiS2), amorphous molybdenum minerals (jordisite, MoS2), bravoite, sphalerite, wurtzite, polydimite, gersdorffite, violarite, millerite, sulvanite, pentlandite, tennanite and as traces native gold, uranitite, tiemannite, arsenopyrite, chalcopyrite and covellite. Discrete platinum group minerals may be unusual. Some ore samples are surprisingly light because of abundant organic matter and large amount of pores.

GANGUE MINERALOGY (Principal and subordinate):

Chert, amorphous silica, phosphatic sediments and bitumen. Can be interbedded with pellets of solid organic matter (called stone coal in China). Barite laths are reported in two of the China deposits.

ALTERATION MINERALOGY:

Siliceous stockworks and bitumen veins with silicified wallrock occur in the footwall units. Carbonate concretions up to 1.5 m in diameter occur immediately below the Nick mineralized horizon in the Yukon.

WEATHERING:

Mineralized horizons readily oxidize to a black colour and are recessive. Phosphatic horizons can be resistant to weathering.

ORE CONTROLS:

The deposits developed in restricted basins with anoxic conditions. Known deposits are found near the basal contact of major formations. Underlying regional unconformities and major basin faults are possible controls on mineralization. Chinese deposits occur discontinuously in a 1600 km long arcuate belt, possibly controlled by basement fractures.

GENETIC MODEL:

Several genetic models have been suggested reflecting the limited data available and the unusual presence of PGEs without ultramafic rocks. Syngenetic deposition from seafloor springs with deposition of metals on or just beneath the seafloor is the most favoured model. Siliceous venting tubes and chert beds in the underlying beds in the Yukon suggest a hydrothermal source for metals.

ASSOCIATED DEPOSIT TYPES:

Phosphorite layers (F07?), stone coal, SEDEX Pb-Zn (E14), Sediment-hosted barite (E17), vanadian shales, sediment-hosted Ag-V, uranium deposits.

COMMENTS:

Ag-V and V deposits hosted by black shales have been described from the same region in China hosted by underlying late Precambrian rocks.

EXPLORATION GUIDES regrese arriba
GEOCHEMICAL SIGNATURE:

Elevated values of Ni, Mo, Au, PGE, C, P, Ba, Zn, Re, Se, As, U, V and S in rocks throughout large parts of basin and derived stream sediments. In China average regional values for host shales of 350 g/t Mo, 150 g/t Ni, several wt % P2O5 and 5 to 22% organic matter. Organic content correlates with metal contents for Ni, Mo and Zn.

GEOPHYSICAL SIGNATURE:

Electromagnetic surveys should detect pyrite horizons.

OTHER EXPLORATION GUIDES:

Anoxic black shales in sub-basins within marginal basins. Chert or phosphate-rich sediments associated with a pyritiferous horizon. Barren, 5 mm to 1.5 cm thick, pyrite layers (occasionally geochemically anomalous) up to tens of metres above mineralized horizon.

ECONOMIC FACTORS regrese arriba
GRADE AND TONNAGE:

The thin sedimentary horizons (not economic) represent hundreds of thousands of tonnes grading in per cent values for at least two of Ni-Mo-Zn with significant PGEs. In China, Zunyi Mo mines yield ~ 1000 t per year averaging ~4 % Mo and containing up to 4 % Ni, 2 % Zn, 0.7 g/t Au, 50 g/t Ag, 0.3 g/t Pt, 0.4 g/t Pd and 30 g/t Ir. The ore is recovered from a number of small adits using labour-intensive mining methods.

ECONOMIC LIMITATIONS:

In China the Mo-bearing phase is recovered by roasting followed by caustic leaching to produce ammonium molybdate. Molybedenum-bearing phases are fine grained and dispersed, therefore all ore (cutoff grade 4.1% Mo) is direct shipped to the smelter after crushing.

IMPORTANCE:

Current world production from shale-hosted Ni-Mo-PGE mines is approximately 1000 t of ore with grades of approximately 4 % Mo. Known deposits of this type are too thin to be economic at current metal prices, except in special conditions. However, these deposits contain enormous tonnages of relatively high grade Ni, Mo, Zn and PGE which may be exploited if thicker deposits can be found, or a relevant new technology is developed.

REFERENCES regrese arriba
  • ACKNOWLEDGEMENTS: Larry Hulbert of the Geological Survey of Canada introduced the senior author to this deposit type and provided many useful comments. Rob Carne of Archer, Cathro and Associates Limited reviewed a draft manuscript.

  • Coveney, R.M., Jr. and Nansheng, C. (1991): Ni-Mo-PGE-Au-rich Ores in Chinese Black Shales and Speculations on Possible Analogues in the United States; Mineralium Deposita, Volume 26, pages 83-88.

  • Coveney, R.M. Jr., Murowchick, J.B., Grauch, R.I., Nansheng, C. and Glascock, M.D. (1992): Field Relations, Origins and Resource Implications for Platiniferous Molybdenum-Nickel Ores in Black Shales of South China; Canadiun Institute of Mining, Metallurgy and Petroleum, Exploration and Mining Geology, Volume 1, No. 1, pages 21-28.

  • Coveney, R. M. Jr., Grauch, R. I. and Murowchick, J.B. (1993): Ore Mineralogy of Nickel-Molybdenum Sulfide Beds Hosted by Black Shales of South China; in The Paul E. Queneau International Symposium, Extractive Metallurgy of Copper, Nickel and Cobalt, Volume 1: Fundamental Aspects, Reddy, R.G. and Weizenbach, R.N., Editors, The Minerals, Metals and Materials Society, pages 369-375.

  • Fan Delian (1983): Poly Elements in the Lower Cambrian Black Shale Series in Southern China; in The Significance of Trace Metals in Solving Petrogenetic Problems and Controversies, Augustithis, S.S., Editor, Theophrastus Publications, Athens, Greece, pages 447-474.

  • Horan, M.F., Morgan, J.W., Grauch, R.I., Coveney, R.M. Jr, Murowchick, J.B. and Hulbert, L.J. (1994): Rhenium and Osmium Isotopes in Black Shales and Ni-Mo-PGE-rich Sulphide Layers, Yukon Territory, Canada, and Hunan and Guizhou Provinces, China; Geochimica et Cosmochimica Acta, Volume 58, pages 257-265.

  • Hulbert, L. J., Gregoire, C.D., Paktunc, D. and Carne, R. C. (1992): Sedimentary Nickel, Zinc and Platinum-group-element Mineralization in Devonian Black Shales at the Nick Property, Yukon, Canada: A New Deposit Type; Canadiun Institute of Mining, Metallurgy and Petroleum, Exploration and Mining Geology, Volume 1, No. 1, pages 39 - 62

  • Murowchick, J.B., Coveney, R. M. Jr., Grauch, R.I., Eldridge, C. S. and Shelton, K.I. (1994): Cyclic Variations of Sulfur Isotopes in Cambrian Stratabound Ni-Mo-(PGE-Au) Ores of Southern China; Geochimica et Cosmochimica Acta, Volume 58, No. 7, pages 1813-1823.

  • Nansheng, C. and Coveney, R. M. Jr. (1989): Ores in Metal-rich Shale of Southern China; U. S. Geological Survey, Circular 1037, pages 7-8.


Cortesia del Gobierno de BRITISH COLUMBIA. Ministerio de Enegia y Minas
Business contact: Commentaries, proposals or details for negotiation: Mr. Jorge Perazzo
51 1 2638212 (spanish please) 1—602-499 2708 (USA)
jperazzo@miningperu.com
Web Design: www.creatimedia.com