A new orogenic gold belt in Southeast Asia: Geology, mineralogy and genesis of the Vangtat gold deposit, Southeastern Laos
A new orogenic gold belt in Southeast Asia: Geology, mineralogy and genesis of the Vangtat gold deposit, Southeastern Laos
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东南亚新的造山金矿带：老挝东南部Vangtat金矿的地质、矿物学和成因
DOI：
10.1111/rge.12283
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发表时间：
2021
期刊：
影响因子：
1.4
通讯作者：
Wong Henry
中科院分区：
文献类型：
--
作者：
Bounliyong Patthana;Arribas Antonio;Watanabe Yasushi;Echigo Takuya;Wong Henry
旺塔特金矿是老挝东南部近20年来发现和开发的新造山金矿带中的主要金矿。我们对旺塔特造山金矿床的研究表明，它形成于波科缝合带西段的会聚边缘，标志着印度支那地体与康图姆地块的碰撞。剪切构造和绿片岩相变质岩是旺塔特金矿化的主要容矿岩石。高品位含金石英硫化物脉体与围岩热液蚀变具有成因联系，蚀变矿物有石英、碳酸盐、石墨、白云母、绿泥石和黄铁矿。流体包裹体和围岩蚀变组合研究表明，旺塔特金矿床形成于低盐度、还原、弱碱性-近中性pH流体，主要由H2O、NaCl、CO2、CH4、N_2、H_2S、H_2、O_2、Si和K组成，金以硫化物络合物形式赋存。金的沉淀与围岩的硫化作用和与含碳主岩的进一步还原有关。毒砂测温法测得的圈闭温度(36 0~395℃)与原生流体包裹体显微测温法测得的均一温度(2 40~2 5 0℃)的相关性表明，旺塔特矿床的压力范围为3 80~42 0 Mpa，深度范围为11~13 Km。金主要以包裹体形式赋存于黄铁矿中，含金黄铁矿的结构、化学和硫同位素组成均一。含金黄铁矿δ34S值变化范围为+4~+6‰，与火成岩的δ34S组成一致。以及来自Vangtat含金黄铁矿的钴/镍比值，它们显著大于1(avg.6.3)，我们认为旺塔特矿床地质基底中的镁铁质-超镁铁质岩石可能是热液金和硫的来源。该造山带金矿床的形成与变质脱水和脱挥发分作用有关，后者将金运移到矿床所在地。
The Vangtat deposit is the major gold deposit in a new orogenic gold belt discovered and developed in southeastern Laos in the past two decades. Our study of the Vangtat orogenic gold deposit shows that it formed within a convergent margin along the western segment of the Poko suture zone, which marks the collision between the Indochina Terrane and the Kontum Massif. Shear structure and greenschist facies metamorphic rocks are the main hosts for gold mineralization in the Vangtat deposit. High‐grade gold‐bearing quartz‐sulfide veins and wall rock hydrothermal alteration are genetically related, and alteration minerals consist of quartz, carbonate, graphite, white mica, chlorite, and pyrite. The study of fluid inclusions and wall rock alteration assemblages indicate that the Vangtat gold deposit was formed by an aqueous‐carbonic, low salinity, reduced, weakly alkaline to near‐neutral pH fluid, mainly composed of H2O, NaCl, CO2, CH4, N2, H2S, H2, O2, Si, and K. Gold was predominantly carried as a sulfide complex. The precipitation of gold is related to wall rock sulfidation and the further reduction with the carbon‐bearing host rock. The correlation between trapping temperature obtained from arsenopyrite geothermometry (360–395°C) and homogenization temperature obtained from primary fluid inclusion microthermometry (240–250°C), indicates a pressure and depth range for the Vangtat deposit of 380–420 MPa and 11–13 km, respectively. Gold appears as inclusions mainly in pyrite, and auriferous pyrite is homogeneous in textural, chemical, and sulfur isotopic composition. Auriferous pyrite δ34S values range from +4 to +6‰, which is compatible with the δ34S composition of igneous rocks. Together with cobalt/nickel ratios from the Vangtat auriferous pyrite, which are significantly greater than one (avg. 6.3), we suggest that mafic‐ultramafic rocks in the geologic basement of the Vangtat deposit are the plausible source of hydrothermal gold and sulfur. The formation of this orogenic gold deposit is associated with metamorphic dehydration and devolatilization that transported gold to the site of deposition.