甘肃两当湘潭子金矿床地质特征及成因

甘肃两当湘潭子金矿位于西秦岭造山带东段,金矿体主要受北西西向断裂控制,与区内发育的中酸性岩脉空间关系密切。显微观察和电子探针分析表明,Au主要赋存在黄铁矿和毒砂中,矿体中黄铁矿Co/Ni特征显示黄铁矿的成因与岩浆作用有关。通过稀土元素分析发现,矿石的稀土元素特征与岩体的稀土元素特征基本一致,而与地层围岩有明显差异。对矿石中的黄铁矿进行硫同位素测试,硫化物δ³⁴S值介于-5.7‰~2.0‰之间,均值为0.38‰,δ³⁴S值频数分布比较集中,具有以近零为中心的塔式分布特征,表明矿石中硫的来源与岩浆作用有关。通过氢氧同位素分析,湘潭子金矿区矿石的δ¹⁸${{\text{O}}_{{{\text{H}}_{2}}\text{O}}}$值介于3.44‰~9.65‰之间,均值为6.29‰,δD介于-120.10‰~-79.00‰之间,均值为-100.47‰,表明本区成矿流体主要来自岩浆水。铅同位素特征显示湘潭子金矿区铅的演化与岩浆作用和造山运动关系密切。通过对比研究可知湘潭子金矿的主成矿时代为印支晚期。湘潭子金矿是印支晚期含成矿物质和流体的岩浆上侵,受浅部断裂系统控制的脉状矿体。湘潭子金矿的发现及成因研究对西秦岭地区找矿方向具有重要的意义。

Geological Characteristics and Genesis of the Xiangtanzi Gold Deposit in Liangdang County,Gansu Province

The Xiangtanzi gold deposit is located in the eastern West Qinling orogenic belt. The gold deposit is mainly controlled by NW-trending faults, and is closely related to the local intermediate-felsic dikes. Microscopic observation and electron microprobe analysis show that Au is mainly hosted in pyrite and arsenopyrite. The Co/Ni characteristics of pyrite in the ore body show that the genesis of pyrite is related to magmatism. Through REE analysis, it is found that REE characteristics of ore are basically consistent with those of rock mass, but obviously different from those of surrounding rock.The sulfur isotope of pyrite in the ore was tested and the ore sulfide δ³⁴S values are from -5.7‰ to 2.0‰ (avg.0.38‰), clustering around zero with a tower distribution, which indicates that the ore sulfur source is magmatic. By hydrogen and oxygen isotope analysis, the Xiangtanzi gold ore has δ¹⁸${{\text{O}}_{{{\text{H}}_{2}}\text{O}}}$=3.44‰-9.65‰ (avg.6.29‰) and δD=-120.10‰ to -79.00‰ (avg.-100.47‰). This indicates that the ore-forming fluid in this area came mainly from magmatic water.Pb isotope characteristics indicates that the Pb evolution at Xiangtanzi was closely related to magmatism and orogeny. A comparative study shows that the metallogenic epoch of the Xiangtanzi gold deposit is late Indosinian. The Xiangtanzi gold deposit is a vein shaped ore body controlled by shallow fault system, which was invaded by magma containing ore-forming materials and fluids in the late Indosinian period. The discovery and genesis of Xiangtanzi gold deposit is of great significance to the prospecting direction in West Qinling area.