山西梨园金矿黄铁矿微量元素及S-Pb-He-Ar同位素地球化学特征及其地质意义

山西梨园金矿是近年华北克拉通内部金矿找矿的新进展,其矿化样式多,具有较高的研究价值。梨园金矿赋存于太古宙阜平群片麻岩和混合岩化花岗岩中,受区内北北东向断裂控制,主要由爆破角砾岩型的1号矿体和石英脉型的2号矿体组成。矿石矿物主要为黄铁矿、方铅矿和闪锌矿等,脉石矿物主要为石英、绢云母、钾长石等,蚀变类型主要为硅化、钾长石化、绢云母化、绿泥石化等。黄铁矿、黄铜矿和闪锌矿δ³⁴S值为0.9‰~4.3‰,平均值为3.0‰,说明硫源主要来自岩浆;方铅矿δ³⁴S值为-12.8‰~1.4‰,平均值为-4.2‰,pH值升高可能是造成方铅矿高负δ³⁴S值的原因。金属硫化物Pb同位素变化范围较小,²⁰⁶Pb/²⁰⁴Pb为16.697~16.890,²⁰⁷Pb/²⁰⁴Pb为15.239~15.267,²⁰⁸Pb/²⁰⁴Pb为42.186~45.334,均落入下地壳演化线附近,表明成矿流体运移过程中可能淋滤了富Th的下地壳物质。黄铁矿的³He/⁴He为0.27~1.04 R_a,⁴⁰Ar/³⁶Ar为1 194.61~5 488.80,³⁸Ar/³⁶Ar为0.204~0.218,表明成矿流体主要来源于地壳,部分来源于地幔流体,具有壳幔混合的岩浆流体特点。微量元素特征显示黄铁矿具有岩浆热液型黄铁矿的特点,辉绿岩脉和石英斑岩的部分物质可能加入了成矿过程。文章认为梨园金矿为与浅成岩浆侵入作用相关的岩浆热液型金矿床,爆破角砾岩型和石英脉型矿体不同的沉淀机制和矿物结晶过程是导致二者REE含量、S-Pb-He-Ar同位素等方面存在差异的主要原因。梨园金矿深部具有寻找细脉浸染型矿体的可能,其成矿作用是太行山中部地区燕山期构造岩浆活动的又一具体表现。

The characteristics of trace elements and S,Pb, He and Ar isotopes in the Liyuan gold deposit in Shanxi Province,and their significance

The Liyuan gold deposit is an exploration breakthrough at the inner North China Craton in recent years. It has many types of mineralization with high research values. The Liyuan gold deposit occurs in the archaean Fuping group gneiss and mixed rocked granite, controlled by the NNE fault in the area, and mainly consists of explosive breccia-type orebody and quartz vein-type orebody. Ore minerals are mainly pyrite, galena and sphalerite, while gangue minerals are mainly quartz, sericite and K-feldspar, and alteration is mainly silicification, K-feldspar, sericitization and chloritization.The δ³⁴S values of pyrite, chalcopyrite and sphalerite are 0.9‰-4.3‰, with an average of 3.0‰, which indicates that the source of sulfur mainly comes from the magma fluids.The δ³⁴S values of galena are -12.8‰-1.4‰, with an average of -4.2‰. The increase in pH value may be the cause of the high negative δ³⁴S value of galena. The variation range of Pb isotopes of metal sulfides is relatively small, and²⁰⁶Pb/²⁰⁴Pb values are 16.697-16.890,²⁰⁷Pb/²⁰⁴Pb values are 15.239-15.267,²⁰⁸Pb/²⁰⁴Pb values are 42.186-45.334, all of which fall near the evolution line of the lower crust. These variations indicate that the ore-forming fluid may have drenched the rich lower crust materials during the migration process. The³He/⁴He of pyrite is 0.27-1.04 R_a,⁴⁰Ar/³⁶Ar is 1194.61-5488.80, and³⁸Ar/³⁶Ar is 0.204-0.218, which indicates that the ore-forming fluid is mainly from the crust and partly from the mantle fluid, with the characteristics of magma fluid mixed with the crust and mantle. The characteristics of trace elements indicate that pyrite has the characteristics of magmatic-hydrothermal pyrite, and some materials of diabase vein and quartz porphyry may have been involved in the mineralization process. In conclusion, the Liyuan gold deposit is considered to be the magmatic-hydrothermal gold deposit related to the shallow magmatic intrusion. And the difference in REE and S-Pb-He-Ar isotopes, between the two types, is mainly due to the different precipitation mechanisms and mineral crystallization processes of the explosive breccia-type and quartz vein-type orebodies. In the deep part of the Liyuan gold deposit, it is possible to search for the veinlet-disseminated orebodies, and its mineralization is another specific manifestation of Yanshanian tectono-magmatic activity in the central Taihang Mountains.