MINERAL ASSEMBLAGES, FLUID INCLUSIONS, PYRITE TRACE ELEMENTS, AND S-O ISOTOPES OF GOLD ORES FROM THE CENOZOIC DAPING DEPOSIT, SW CHINA: IMPLICATIONS FOR THE GENESIS OF COMPLEX OROGENIC LODE GOLD SYSTEMS

IF 5.5 1区地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS

Economic Geology Pub Date : 2023-03-01 DOI:10.5382/econgeo.4995

Lin Yang, Qingfei Wang, D. Groves, Huajian Li, D. Zhai, Xuan Wang, Jun Deng

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引用次数: 7

Abstract

The Cenozoic Daping orogenic gold deposit, on the southeastern margin of the Tibetan Plateau, China, contains four lode types that contain a total of 55 t gold. Pyrite-chalcopyrite–dominated (VA) and galena-dominated polymetallic sulfide veins (VB) hosted by Neoproterozoic diorite are associated with quartz-sericite-chlorite ± epidote (± barite in VB veins) alteration. Pyrite-dominated (VC) and pyrite-pyrrhotite–dominated veins (VD) hosted by Silurian dolostone (intercalated with carbon-bearing argillaceous limestone in VD veins) are related to ankerite-siderite-quartz ± sericite alteration. All have free gold spatially and temporally associated with pyrite, chalcopyrite, galena, pyrrhotite, or quartz. Most VA and VB veins are controlled by steeply SW-dipping ductile-brittle shear zones with jigsaw wall-rock breccias in VB veins, whereas gently SW-dipping faults host VC and VD veins. There are some significant differences between different veins: (1) there were more acidic mineralization conditions for VA and VB veins relative to VC and VD veins, and more oxidized conditions for VB veins relative to other veins; (2) pyrite is rich in Co-Ni in VA and VB veins, compared to enrichment in As-Au for VC and VD veins; (3) sulfide δ34S values of 3.2 to 11.8‰ (median 8.2‰) for VA, VC, and VD veins contrast with −4.6 to +0.9‰ (median 0‰) for VB veins. The contrasting mineral parageneses, pH values, and pyrite geochemistry can be attributed to fluid-rock interaction as evidenced by replacements of amphibole by sericite in diorite and dolomite by ankerite and siderite in dolostone. The lower (~8‰) VB sulfide δ34S values and interpreted fluid oxidation relative to other veins, together with the presence of breccias and barite, can be explained by phase separation due to flash vaporization triggered by extreme hydrofracturing. The consistent NW-trending vein sets, similar median S-O isotope ratios of original ore fluids, and lack of multistage overlap of gold mineralization and alteration zones support a single-source fluid for gold mineralization at Daping. This study is diagnostic rather than just indicative in that it systematically and quantitatively portrays the mineralization diversity in an orogenic gold system formed by a single-source fluid regulated by the external fluid-rock interactions and internal hydrofracturing.

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新生代大坪金矿矿石的矿物组合、流体包裹体、黄铁矿微量元素和s-o同位素:对复杂造山脉金系统成因的启示

中国青藏高原东南缘新生代大坪造山带金矿床有4种矿脉类型，含金总量为55 t。以新元古代闪长岩为寄主的黄铁矿-黄铜矿(VA)和方铅矿-多金属硫化物(VB)脉与石英-绢云母-绿泥石±绿帘石(VB脉中±重晶石)蚀变有关。志留系白云岩赋存的黄铁矿为主(VC)和黄铁矿-磁黄铁矿为主(VD脉中嵌有含碳泥质灰岩)与铁菱铁矿-石英±绢云母蚀变有关。所有的游离金在空间和时间上都与黄铁矿、黄铜矿、方铅矿、磁黄铁矿或石英有关。VA和VB脉体主要受急西倾韧性-脆性剪切带控制，VB脉体中发育锯齿状围岩角砾岩，而缓西倾断裂则主要发育VC和VD脉体。不同矿脉间存在显著差异:(1)VA、VB矿脉相对VC、VD矿脉具有更多的酸性矿化条件，VB矿脉相对于其他矿脉具有更多的氧化条件;(2)黄铁矿在VA和VB脉中富集Co-Ni，而在VC和VD脉中富集As-Au;(3) VA、VC、VD矿脉的硫化物δ34S值为3.2 ~ 11.8‰(中值8.2‰)，VB矿脉的δ34S值为- 4.6 ~ +0.9‰(中值0‰)。闪长岩中闪长岩中绢云母取代角闪孔，白云岩中铁云母取代云母，白云岩中菱铁矿取代白云石，这些对比鲜明的矿物共生、pH值和黄铁矿地球化学可归因于流体-岩石相互作用。与其他矿脉相比，VB硫化物δ34S值较低(~8‰)，解释流体氧化，同时存在角砾岩和重晶石，可以用极端水力压裂引发的闪蒸引起的相分离来解释。一致的北西向矿脉组、相似的原始成矿流体S-O同位素比值中值、金矿化与蚀变带缺乏多期重叠，支持大坪金矿成矿流体来源单一。本研究系统、定量地描绘了受外部流岩相互作用和内部水力压裂调节的单一源流体形成的造山带金系统的矿化多样性，具有诊断意义，而不仅仅是指示意义。

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来源期刊

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.