甘肃岷县寨上金矿床地质特征及成因初探

Geological features and genetic analysis of Zhaishang gold deposit, Min county, Gansu

寨上金矿床位于西秦岭岷-礼前渊盆地西侧南部,发育在不同岩性和不同粒度组成海底斜坡扇环境下的浊积岩系中。主要的含矿建造为晚泥盆系e组的一套沉积岩系。岩石具有碳-钙-泥质沉积岩高频叠置组合。控矿构造属于韧性-脆性递进剪切变形构造性质,该构造呈NWW向延伸,南倾,倾角30°～50°,具有递进多期多阶段活动的特点,是本区控矿和成矿的主要决定因素。含矿围岩热液蚀变作用微弱,主要表现为浸染状、细脉状-浸染状的含砷黄铁矿化、毒砂化、微细脉与细网脉状硅化、铁白云石化,均与金矿化密切相关。矿石构造以微细粒稀疏浸染状构造、微细脉-稀疏浸染状构造、团块-浸染状构造、草莓状构造为主,矿石结构以自形-半自形微细粒状结构、半自形-他形粒状结构、增生环带结构、包含结构为主。矿区发现了南、北两个矿带,北矿带主要发育黄铁矿型金矿体、黄铁矿-毒砂型金矿体、锑-金型金矿体;南矿带主要发育铜金矿体。因此认为,①中泥盆统e组细碎屑岩-碳酸盐岩为本区矿源层;②寨上金矿区控矿构造属于韧-脆性递进剪切变形构造性质,具有递进多期多阶段活动的特点,是本区控矿和成矿的主要决定因素;③含砷黄铁矿、毒砂的增生环带,是由含砷低的黄铁矿或毒砂内核和含砷较高的黄铁矿或毒砂增生环带构成;④矿床具有后生中低温热液特点,将寨上金矿确定为经典卡林型矿床类型。

Zhaishang gold deposit lies on the south of Li-Min fore deep basin in the West Qinling, which is make up of the turbidite with the different lithology and granularity in the seabed slope fan envronment. Ore field is located in e group stratigraphic formation of Middle Devonian series. Rocks have the characteristics of high frepuency fold, which are make up of carbonaceous slate, sandstone, marlite orebearing rock seriea. We can conclude that Zhaishang gold deposit is controlled by the structure of ductilebrittle shear belt, along NWW-trenching, obliquity 30～50°, and Have the character of multiphases and polystages. Ductile-brittle shear belt is the main ore-controlling factors in Zhaishang gold deposit. Orebearing wall rock have the weak hydrothermal alteration, mainly present disseminated, stringer veindisseminated arsenical pyritization, micro-stringer vein and stringer network vein siliconization, ankeritization, which are associate with Au. Ore structures have micro-disseminated, micro-stringer vein, congloeration disseminated, strawberry, and ore frames have automorphic-hypautomorphic granular, allotriomorphic granular, etc in late stage. Main industrial ore body occurs in the transition and alternation position of carbonaceous microclastic rocks and carbonaceous marlite, which are composed of two ore straps, southern, northern straps respectively. Northern ore strap is main industrial ore body, which have pyrite, pyrite-atsenopyrite, Sb-Au type gold ores the main ore body is Cu-Au type gold in the southen strap. Above all, we can draw a conclusion ：①we regard e group stratigraphic formation of Middle Devonian series as the ore source of Zhaishang gold deposit;②the ore-controlling structure of Zhaishang gold deposit is ductile-brittle shear belt, and it has the character of multiphases and polystages, which is the main ore-forming and ore-controlling factors;③arsenopyrite and arsenobearing pyrite growth-bands is composed of the low arseno-breaing pyrite or arsen-opyrite in the kernel and the high arseno-breaing pyrite or arsen-opyrite growth-bands ;④the gold deposit has character of low-middle temperature hydrothermal, we define Zhaishang gold deposit as calin-type gold deposit.