| 扬子板块北缘马元铅锌矿地球化学特征及成矿机制探讨 |
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| 引用本文：刘淑文,李荣西,刘云华,曾荣.2016.扬子板块北缘马元铅锌矿地球化学特征及成矿机制探讨[J].地球学报,37(1):101-110. |
| DOI：10.3975/cagsb.2016.01.10 |
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| 基金项目:中国地质调查局项目(编号: 1212011121117) |
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| 中文摘要:位于扬子板块北缘的马元铅锌矿呈似层状产于震旦系灯影组角砾状白云岩中, 矿石矿物为闪锌矿、方铅矿, 脉石矿物有白云石、重晶石和少量石英、萤石、方解石等。本文着重对主要矿石及脉石矿物的锶、硫同位素和稀土元素地球化学特征进行对比研究, 以探讨其成矿机制。早期沉淀产物闪锌矿流体包裹体及白云石的87Sr/86Sr比值为0.71111~0.71241, 表明Sr来源以壳源锶为主; 晚期重晶石87Sr/86Sr比值为0.70918和0.70971, 表明重晶石中的锶主要来源于海水锶, 有少量壳源锶加入。早期产物白云石、闪锌矿和方铅矿的稀土元素具有类似热卤水特征的明显正Eu异常(去掉特高值后平均值为1.99), 而晚期重晶石则具有类似海水特征的负Ce异常(0.26)。硫同位素表现出富重硫(δ34S>12‰)的特点, 表明硫可能主要来源于海相硫酸盐。还原硫的形成机制为硫酸盐的热化学还原作用, 有机质如甲烷可能充当了还原剂。闪锌矿、方铅矿及重晶石的δ34S值各自集中分布在较小的范围内且同位素分馏达到平衡, 暗示金属、还原硫和硫酸根可能是同一成矿流体搬运的。矿质沉淀机制可能是地层中循环的富含放射性锶以及多种金属元素的成矿热卤水与下渗的海水(或大气降水)混合导致的。早期沉淀白云石、闪锌矿以及方铅矿的流体以热卤水为主, 晚期与重晶石沉淀有关的流体则具有相对富含海水(或大气降水)的特点。 |
| 中文关键词:硫同位素 锶同位素 REE 成矿机制 马元铅锌矿 |
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| Geochemical Characteristics and Metallogenic Mechanism of the Mayuan Pb-Zn Deposit on the Northern Margin of Yangtze Plate |
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| Abstract:The Mayuan stratabound Pb-Zn deposit in Nanzheng of Shaanxi Province is located on the northern margin of the Yangtze Plate, and the orebodies are stratiform and hosted in breciated dolostone of the Sinian Dengying Formation. The ore minerals are mainly sphalerite and galena, and the gangue minerals comprise dolomite, barite, and small amounts of quartz, fluorite and calcite. This study mainly focused on the strontium, sulfur isotopes and the rare earth elements of the major ore and gangue minerals for the purpose of investigating the metallogenic mechanism. The 87Sr/86Sr ratios of the early precipitation product dolomite and the fluid inclusions of sphalerite range from 0.71111 to 0.71241, suggesting that Sr was derived from the crust, that is, ore-forming fluid had flowed through the basement and the Paleozoic clastic rocks which had a high 87Sr/86Sr ratios. Besides, the two 87Sr/86Sr ratios (0.70918 and 0.70971) of the late precipitation product barite imply that strontium mainly came from seawater with the addition of a small amount of crust materials. The rare earth elements of the early product of dolomite, sphalerite and galena are characterized by obvious Eu anomaly of the hot brine, while the late barites by the negative Ce anomaly of the sea water. The δ34S values show that heavy sulfur is abundant (δ34S>12‰), and that the sulfur might have been derived from marine sulfate. The formation mechanism of the reduced sulfur was the thermochemical sulfate reduction, and the organic matter, such as methane, might have acted as a reductant. The δ34S values of sphalerite, galena and barite are all concentrated in a narrow range and, what is more, the sulfur isotope fractionation has reached equilibrium, which might imply that the reduced sulfur, metal cations and the sulfate ions might have been transported by the same fluid. The mineral precipitation of the Mayuan Pb-Zn deposit resulted probably from the mixing of the seawater (or meteoric water) and the hot brine which circulated in the basin and was enriched in radioactive strontium and metal elements. The fluid related to the early dolomite, sphalerite and galena precipitation was mainly associated with the hot brine, whereas the fluid related to late barite precipitation was relatively enriched in seawater (or atmospheric water). |
| keywords:sulfur isotope strontium isotope REE metallogenic mechanism Mayuan Pb-Zn deposit |
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