甘肃阳山金矿床矿石特征及成因意义

甘肃阳山金矿床是一个超大型细脉浸染型金矿床,所处大地构造位置属西秦岭成矿带,位于中朝板块、扬子板块及松潘-甘孜褶皱系夹持的区域内。其矿体产于燕山期斜长花岗斑岩与中泥盆统三河口组千枚岩接触带及围岩构造破碎带内。通过显微镜下鉴定、电子探针、矿石成分分析等方法,对矿石结构构造、矿石化学成分和矿物成分、载金矿物和金的赋存状态进行研究,发现其主要的载金矿物为岩浆热液成因的黄铁矿,生物化学沉积成因的黄铁矿对成矿物质的富集及矿源层的形成起重要的作用,中泥盆统三河口组为矿源层。矿石结构构造反映出矿床的形成经历了沉积成矿作用和热液成矿作用,成矿过程为多期多阶段。稳定同位素研究表明,成矿物质来源于矿源层及燕山期岩浆岩。矿床成因类型为中低温岩浆热液层控型金矿床。

Ore characteristics of the Yangshan gold deposit in Gansu Province and its genetic significance

The Yangshan gold deposit in Gansu Province is located in the east of Songpan-Ganzi fold system and is a large-sized disseminated gold deposit. Field investigation reveals that the orebody occurs in the internal or external contact zones between plagioclase granite porphyry dikes of Yanshannian period and phyllite of Shanhekou Formation of Middle Devonian period as well as in the shatter zone of the wall rocks. Microscope identification, electron microprobe analysis and ore composition analysis were carried out to study the ore fabrics, mineral compositions and gold occurrence in the ore systematically and thoroughly. The authors found that the pyrite of hydrothermal genesis was the main gold-bearing mineral and the pyrite was genetically formed by biochemical sedimentation which had played an important role in the formation of mineral deposits and enrichment of metallogenic materials; the authors also found that the source bed was Middle Devonian Shanhekou Formation. The ore texture and structure show that the formation of the gold deposit experienced sedimentation and hydrothermal mineralization with multiple stages during the ore-forming process. Studies of stable isotopes show that the major metallogenic matters came from the source bed and Yanshannian magmatite. The result indicates that the deposit is a stratabound gold deposit related to medium-low temperature magmatic hydrothermal activities.