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Magmatic deposits—sulfides (Ni and Cr) + PGE PowerPoint Presentation
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Magmatic deposits—sulfides (Ni and Cr) + PGE
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  1. Magmatic deposits—sulfides (Ni and Cr) + PGE

  2. Alkali feldspars at low pressures: two complete solid solutions with a solvus Immiscibility field

  3. 礦物種類 分子式 含銅量(%) 自然銅 Native Copper Cu 100 黃銅礦 Chalcopyrite CuFeS2 34.5 斑銅礦 Bornite Cu5FeS4 63.3 輝銅礦 Chalcocite Cu2S 79.8 銅 藍 Covellite CuS 66.4 硫砷銅礦 Enargite Cu3AsS4 48.3 砷黝銅礦 Tetrahedrite (Cu,Fe)12As4S13 57.0 黝銅礦 Tennantite (Cu,Fe)12Sb4S13 52.1 赤銅礦 Cuprite Cu2O 88.8 黑銅礦 Tenorite CuO 79.8 孔雀石 Malachite CuCO3.Cu(OH)2 57.3 藍銅礦 Azurite2 CuCO3.Cu(OH)2 55.1 銅靛礬 Chalcocyanite CuSO4 膽礬 Chalcanthite CuSO4.5H2O 銅葉綠礬 Cuprocopiapite CuFe43+(SO4)6(OH)2.20H2O 矽孔雀石 Chrysocolla CuSiO3.2H2O 36.0

  4. 礦物名 化學式 鎳含量 針鎳礦 (Millerite) NiS 鎳黃鐵礦 (Pentlandite) (Fe,Ni)9S8 ( Co 達1-3%), Pt, Pd 紫硫鎳鐵礦 (Violarite) FeS.Ni2S3 紅砷鎳礦 (Nickeline) NiAs 輝砷鎳礦 (Gersdorffite) NiAsS 紅銻鎳礦 (Breithauptite) NiSb 鎳纖蛇紋石 (Garnierite) Ni(Si4O10)(OH)4.4H2O (NiO<46) 鎳綠泥石 (Nimite) (Ni,Mg)6(Si4O10)(OH)8 鎳綠高嶺石 (Ni-Nontronite) (NiO=1-2) 鎳華 (Anrabergite) Ni3(AsO4).8H2O (NiO=37)

  5. Characteristics of PGE in magmatic processes 鉑族金屬(platinum group elements,簡稱PGE)包括釕(Ru)、銠(Rh)、 鈀(Pd)、鋨(Os)、銥(Ir)、鉑(Pt)六個元素。其中釕、銠、鈀為輕鉑族金屬 (比重11~12),鋨、銥、鉑稱為重鉑族金屬(比重21.4~22)。鉑族金屬 的合金具有耐高溫、耐磨擦的特性。在高溫下強度大,具有高延展性和 低膨脹系數,熱電的穩定性好。 鉑族元素具有親鐵性,鈀、鉑、銠還具有親硫性,尤以鈀最明顯,因此易 與鐵、鎳、鉛、銅、錫形成金屬鍵的化合物。Os、Ru、Ir高價離子易與 硫、砷、銻、鉍、碲、硒等形成離子鍵化合物。在自然界鉑族元素獨立礦 物較少,常見的有自然鉑和鉑族元素互化物。 鉑族元素在地函中含量較高,隕石內的含量平均為:Pt 2.0g/t,Pd 1.3g/t, Os 1.0g/t,Ir 0.7g/t,Rh 0.5g/t,Ru 1.3g/t。在地殼中,鉑族元素多富集於 基性、超基性岩石中。在岩漿結晶分化作用過程中,鉑族金屬主要富集 於鎂鐵質橄欖岩及純橄欖岩中,與鉻鐵礦共生;在蘇長岩、輝長岩中則 與銅鎳硫化物緊密伴生。

  6. Sudbury, Ontario

  7. SUDBURY MINING CAMP To date, the Sudbury mining camp has produced in excess of 16 billion pounds of nickel, 15 billion pounds of copper, 85 million ounces of silver, 17 million ounces of platinum, and 3 million ounces of gold and remains, to this day, Canada’s principal producer of platinum. Currently, there are 35 producing mines in the Sudbury Camp.

  8. GEOLOGY OF THE SUDBURY REGION • The Sudbury region is dominated by a large 60 km long by 30 km wide elliptical depression known as the Sudbury Structure which lies at the junction of three unique geological-structural provinces: the granitic & gneissic basement rocks of the Archean Superior Province to the north, the supracrustal metasediments and metavolcanics of the Early-Proterozoic Southern Province to the south, and the Middle-Proterozoic Grenville Front Tectonic Zone.

  9. GEOLOGY OF THE SUDBURY STRUCTURE • The Sudbury Structure constitutes the largest known concentrations of nickel-copper-PGE bearing sulfide minerals in the world. Due to its economic importance, the structure is one of the most intensively studied and documented regions of the Canadian Shield. • Stratigraphically, from top to bottom, the Sudbury Structure consists of the Whitewater Group of sediments, the underlying Sudbury Igneous Complex (“SIC”), and brecciated footwall rocks surrounding the SIC.

  10. The Whitewater Group • Infilling the central depression of the Sudbury Structure are the Whitewater Group sediments that consist of, from top to bottom: • the Chelmsford Formation greywacke, • the Onwatin Formation manganese-rich slate, • and the Onaping Formation volcaniclastic/breccia sequence.

  11. The Sudbury Igneous Complex Underlying the Whitewater Group is the Sudbury Igneous Complex (“SIC”). The SIC consists of a lower zone of augite-bearing norite; a thin middle layer (Transition Zone) consisting of norite grading upwards into quartz gabbro; and an upper zone of micropegmatite/granophyre. At the base of the lower zone is a discontinuous zone of inclusion and sulfide-rich norite-gabbro commonly known as the Contact Sublayer (“Sublayer”). The Sublayer occurs as gently dipping sheets or irregular lenses along the base of the SIC or as small bodies in radial depressions or troughs in the base of the SIC called embayments, and as steeply dipping dikes called offsets which intrude into the adjacent footwall. The Sublayer is typically gabbroic in the base of the SIC and in the embayments, and typically quartz-diorite in the offset dikes. All Ni-Cu-PGE deposits of the Sudbury Structure are contained within the Sublayer and related structures such as the offset dikes.

  12. There are two types of offset dikes: • 1. radial, which appear to stem directly from the Sublayer • and intrude into the footwall rocks radially away from the SIC. • 2. concentric dikes, which are thought to be related to ring • faults and may be connected to the Sublayer at depth or • represent accumulations of melt rock associated with • pseudo-tachylyte formation.

  13. Origin of the Sudbury Structure • Existing evidence for the origin of the Sudbury Structure supports a meteorite impact. This includes: the irregular and dike-like bodies of pseudo-tachylyte breccias (Sudbury and Footwall breccias) up to 70 km from the margins of the structure; shatter cones in rocks marginal to the structure; the 1.8 km-thick volcaniclastics/breccias of the Onaping formation (interpreted as fallback breccia); and shock deformation lamellae in quartz and feldspar in country rock inclusions within the Onaping formation. The following summarizes the evolution of the Sudbury area.

  14. MINERALIZATION AND DEPOSIT TYPES OF THE SUDBURY STRUCTURE • Sudbury ores are typically zoned. Fractional crystallization of a monosulfide solid solution from a sulfide melt is believed to have given rise to a cumulate phase rich in Fe, Co, Rh, Ru, Ir and Os (pyrrhotite-rich ores) and a fractionated liquid rich in Ni, Cu, Pt, Pd, and Au (chalcopyrite and PGE-rich ores). In some cases, the liquid phase is then believed to have migrated out from the Sublayer and further fractionated to form Cu and PGE rich footwall ores. • Common Ni and Cu-ore minerals consist of pyrrhotite, pentlandite, chalcopyrite with minor pyrite, and cubanite (CuFe2S3). • Sudbury Ni-Cu-PGE sulfide mineralization occurs in three deposit settings:

  15. Contact deposits or “embayment” deposits • Located along the lower contact of the SIC in association with the norite-gabbro inclusion-bearing Sublayer. The Sublayer may be up to 100 metres thick. The greatest thicknesses are found in kilometer-size radial embayments within which are smaller, secondary troughs or “terraces”. The highest sulfide concentrations in the Sublayer are found within these embayments where sulfide distribution is further controlled by the terraces. Large concentrations of sulfides and nickel are often found in footwall deposits immediately adjacent to the terraces. Cu/Ni ratios are typically lowest in the Sublayer and increase towards the Footwall Breccia. • The Sublayer constitutes a well defined exploration target and has been a prolific producer over the years. Consequently contact deposits comprise 21 of the 35 mines in the Sudbury area. Contact deposits at the base of the SIC are still currently being mined by both Falconbridge and Inco at the Falconbridge, Garson and Levack mines.

  16. Footwall deposits • Zones of sulfide mineralization in the form of stringers, veins, massive sheets and/or disseminated sulfide which appear to have migrated outwards from the Sublayer and/or Footwall Breccia and penetrated deeply into the footwall rocks. The Frood-Stobie Mine, which is estimated to have originally contained a geologic resource of 450 to 500 million tonnes, is the largest and best example of a footwall deposit. This mine lies at the east end of the South Range Breccia Belt and is situated almost 2 km into thefootwall. • Offset Dike deposits • Associated with radial and concentric quartz-diorite dikes that extend from the Sublayer into the footwall rocks. Mineralization typically occurs as disseminated to massive sulfides within the dikes. The massive sulfide bodies are often rimmed by a halo of disseminated material that is often found along the contacts of the dike. Examples of offset deposits include Nickel Offsets along the Foy Offset dike, and the Copper Cliff North and South mines and the Totten Mine along the Copper Cliff Offset and Worthington Offset dikes, respectively.

  17. Great Dyke: 330 mile long, 4 mile wide, consists of layers of ultrabasic rocks now largely altered to serpentine. The dyke deposits are bands of chromite about 8 inches thick. Stillwater, Montana: an E-W belt about 50 km long and 1 km wide. Muskox, NW Territories: a Pre-Cambrian layered ultramafic complex.