甘肃大水闪长岩型金矿床地质地球化学特征

Geological and Geochemical Characteristics of Dashui Diorite-type Gold Deposit in Gansu Province

大水金矿床产在闪长岩体内和接触带以及附近灰岩中,地表广泛分布闪长岩脉和红褐色赤铁矿化灰岩,氧化带下部发育大量的微细粒浸染状、细脉状黄铁矿。黄铁矿中微量元素Co/Ni比值范围为1~5,与岩浆成因的黄铁矿Co/Ni比值相吻合;各种矿石稀土元素配分曲线与闪长岩脉接近,而与地层灰岩差别较大,揭示成矿物质的来源与闪长岩脉有关;黄铁矿的3δ4S为-1.8‰^+4.1‰,平均+2.4‰,反映为深源硫;方解石的氢氧同位素分析表明成矿流体主要来源于岩浆水,后期有改造的大气降水参与。地质地球化学特征研究表明,大水金矿床是以闪长岩为主要成矿物质来源,以岩浆水为主要成矿流体的富硫化物的闪长岩型金矿床。

Dashui gold deposit occurs in the diorite and the contact zone as well as surrounding limestone. Diorite veins and red-brown hematized limestone are widely distributing in the surface. Large amounts of fine disseminated and veinlet pyrites occur in the lower oxidized zone in the gold deposit. The Co/Ni ratios range from 1 to 5, close to the pyrite formed by magmatism. The REE pattern describes that gangue minerals are close to diorite veins, but quite different from limestone. Thus, REE geochemistry indicates that the ore-forming materials mainly came from diorite veins closely related to tectono-magmatism. The δ^34S values of pyrite range from - 1.8‰ to ＋ 4.1‰ with a mean of ＋ 2.4‰, reflecting a deep source of sulfur. Samples analyzed for hydrogen and oxygen isotopic compositions of the calcites oreforming fluids were mainly magmatic water, and might be the product of mixing of meteoric water and magmatic water at the late mineralization stage. Studies on geological and geochemical characteristics show that Dashui gold deposit derived its ore-forming materials from the hosted diorite, the ore-fluids were largely magmatic water, as sulfides-rich diorite-type gold deposit.