坦桑尼亚南部姆贝萨探矿区的铜金铂族元素矿化:非常规岩浆硫化物

IF 5.5 1区 地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS Economic Geology Pub Date : 2024-05-01 DOI:10.5382/econgeo.5068
Hidaya Hassan, Jacob Kaavera, Akira Imai, Kotaro Yonezu, Thomas Tindell, Kenzo Sanematsu, Koichiro Watanabe
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引用次数: 0

摘要

最近在坦桑尼亚南部的姆贝萨探矿区发现了高品位铜矿化,但对其成因却知之甚少。在此,我们提供了新的主要元素、微量元素、稀土元素和铂族元素地球化学和岩石学数据,以确定矿化的起源。硫化物矿化主要以黄铜矿和辉铜矿为主,块状矿石和浸染状矿石中的铜/镍含量超过 100。矿化物中缺乏黄铁矿和红柱石,而这两种矿物在岩浆型镍-铜-铂铑矿床中很常见。存在的铂族矿物是微晶石(PdBiTe)和苏德贝里石(PdSb)。在块状矿石和浸染状矿石中,以 Pd + Pt + Au 表示的 PGE 浓度分别高达 1.31 和 1.04 ppm。黄铜矿分离物的δ34S 在-3.9 到-0.6‰之间,辉铜矿分离物的δ34S 在-1.8 到 1.1‰之间,辉铜矿-黄铜矿混合物的δ34S 在-1.3 和 0.6‰之间,大部分与岩浆硫源一致。硫化物赋存于粗粒斜长闪长岩和角闪长片麻岩中,其重结晶纹理显示出变质作用。这两种岩石的特点是富含大离子亲岩元素(LILEs),Zr和Nb呈负异常,这与次大陆岩石圈地幔(SCLM)部分熔融产生的岩浆受到地壳污染一致。硫化銅與碳酸鹽和磷灰石的密切關聯進一步說明了次大陸岩石圈地幔的來源。据认为,硫化物是从浅地壳层富含中间固溶体(iss)的分馏富铜硫化物熔体中结晶出来的。硫化物很可能是以附着在二氧化碳气相上的液滴形式移动的,这一点从碳酸盐和磷灰石与富铜硫化物的密切联系中可以看出。在姆贝萨探矿区周围更深的地方,富含镍的硫化物可能仍未被发现。
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Cu-Au-Platinum Group Element Mineralization in the Mbesa Prospect, Southern Tanzania: Unconventional Magmatic Sulfides
High-grade Cu mineralization was recently discovered in the Mbesa prospect in southern Tanzania, but its origin is poorly constrained. Herein, we present new major element, trace element, rare earth element (REE), and platinum group element (PGE) geochemistry and petrographic data to constrain the origin of the mineralization. The sulfide mineralization is dominated by chalcopyrite and bornite and characterized by high Cu/Ni over 100 in the massive and disseminated ores. The mineralization lacks pyrrhotite and pentlandite, which are found commonly in magmatic Ni-Cu-PGE sulfide deposits. Platinum group minerals present are michenerite (PdBiTe) and sudburyite (PdSb). PGE concentrations expressed as Pd + Pt + Au are up to 1.31 and 1.04 ppm in the massive and disseminated ores, respectively. The δ34S of chalcopyrite separates range from –3.9 to –0.6‰, bornite separates vary from –1.8 to 1.1‰, and bornite-chalcopyrite mixtures yield –1.3 and 0.6‰, mostly consistent with a magmatic sulfur origin. The sulfides are hosted by coarse-grained plagioclase amphibolite and hornblende gneiss with recrystallization textures suggestive of metamorphism. Both rocks are characterized by enrichment in large ion lithophile elements (LILEs), with negative anomalies of Zr and Nb, consistent with crustal contamination of magmas derived from partial melting of subcontinental lithospheric mantle (SCLM). An SCLM origin is further suggested by the close association of Cu sulfides with carbonates and apatite. It is suggested that the sulfides crystallized from the fractionated Cu-rich sulfide melt enriched in intermediate solid solution (iss) at shallow crustal levels. Sulfide were likely mobilized as droplets attached to CO2 vapor phase as expressed by close association between carbonates and apatite with the Cu-rich sulfides. Nickel-rich sulfides may remain undiscovered at deeper portions around the Mbesa prospect.
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来源期刊
Economic Geology
Economic Geology 地学-地球化学与地球物理
CiteScore
10.00
自引率
6.90%
发文量
120
审稿时长
6 months
期刊介绍: The journal, now published semi-quarterly, was first published in 1905 by the Economic Geology Publishing Company (PUBCO), a not-for-profit company established for the purpose of publishing a periodical devoted to economic geology. On the founding of SEG in 1920, a cooperative arrangement between PUBCO and SEG made the journal the official organ of the Society, and PUBCO agreed to carry the Society''s name on the front cover under the heading "Bulletin of the Society of Economic Geologists". PUBCO and SEG continued to operate as cooperating but separate entities until 2001, when the Board of Directors of PUBCO and the Council of SEG, by unanimous consent, approved a formal agreement of merger. The former activities of the PUBCO Board of Directors are now carried out by a Publications Board, a new self-governing unit within SEG.
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