摘要
大桥金矿床位于岷县北一宕昌北大断裂与窑上-石峡大断裂之间。金矿化严格受三叠系下部建造层下岩性段（Ta-1）硅质角砾岩的控制。硅质角砾岩呈层状产出，层位稳定。矿石为有机质含量高并具有黄铁矿化的硅质角砾岩，其黄铁矿环带发育。硅质角砾岩和纹层状硅质岩在稀土元素配分图上未表现出热水沉积的特征，其Fe／Ti-Al／（Al＋Fe＋Mn）图解及SiO2与Al2O3呈负相关以及Sr／Ba值小于1说明，硅质角砾岩和纹层状硅质岩为陆源碎屑沉积成因，进而表明，大桥金矿床不是热水沉积型金矿床。依据环带状黄铁矿和脉状黄铁矿的发育及其高Co／Ni值，可以判断在该矿床形成过程中，热液起到重要作用。黄铁矿的δ34S值为4．21‰～9．82‰，说明其硫来自岩浆硫与地层硫的混合或变质流体。矿石内石英脉中流体包裹体的均一温度为270-310℃，属于中温范围，而硅质角砾岩的元素聚类分析表明Au与低温元素Hg、As密切相关，说明温度降低可能是成矿机制之一。大桥金矿床应属于中一低温热液型金矿床。
The Daqiao gold deposit lies between the Minxian-Dangchang fault and the Yaoshang-Shixia fault. Its gold mineralization exists in the lower lithologic member of lower Triassic formation bed, in which the siliceous breccia presents itself in the bedded form. Ores are pyritized siliceous breccia with high organic carbon content, and pyrite zones are well developed. Siliceous breccia and layered siliceous rocks do not show characteristics of hot- water sedimentary origin in REE patterns. The features of the Fe/Ti-Al/（Al＋Fe＋Mn）diagram and the phe- nomena that SiO2 is negatively correlated with A1203 and Sr/Ba〈 1 indicate that siliceous breccia and lamellar siliceous rocks are clastic sediments. The authors thus hold that the Daqiao gold deposit is not of the hot-water sedimentary type. Zonal pyrite, well developed pyrite veins and high Co/Ni ratios suggest that hydrothermal so- lution played an important role in the formation of the ore deposit.δ34S values of pyrites are in the range of 4.21‰～9.82‰, implying that the sulfur fluids were derived from mixed magmatic and stratigraphic sulfur or from metamorphic fluids. The homogenization temperature of fluid inclusions in quartz is mainly between 270℃ and 310℃, belonging to medium temperature. Cluster analysis of siliceous breccia elements shows that Au is closely related to low temperature elements Hg and As, suggesting that the decrease of temperature might have been one of the mechanisms for gold mineralization. The Daqiao gold deposit is a middle-low temperature hy- drothermal gold deposit.
出处
《矿床地质》
CAS
CSCD
北大核心
2011年第6期1085-1099,共15页
Mineral Deposits
基金
地质过程与矿产资源国家重点实验室自主项目"西秦岭地区构造-岩浆活动与成矿作用"资助
关键词
地质学
硅质角砾岩
环带状黄铁矿
热水沉积型金矿床
中-低温热液型金矿床
西秦岭
甘肃
geology, siliceous breccia, zonal pyrite, hot-water sedimentary gold deposit, middle-low ternperature hydrothermal gold deposit, West Qinling, Gansu Province
