粤中三水盆地长坑金矿赋金硅质岩特征及形成研究

Characteristics and genesis of Changkeng gold-hosting siliceous rock in the rim of southwestern Sanshui Basin,middle Guangdong Province,China

粤中三水盆地长坑赋金硅质岩主要呈层状分布于下石炭统梓门桥组生物碎屑灰岩与上三叠统碳质泥岩(或下石炭统梓门桥组粉砂岩)之间,厚度1～50m,主要由层状、块状及角砾状硅质岩组成。金矿主要呈细脉浸染状产于角砾状硅质岩中。长坑赋金硅质岩层具纹层状构造特征,在其中发现放射虫、微体古生物化石,角砾长轴与硅质纹层平行分布,含有草莓状黄铁矿,这些特征以及长坑金矿床与富湾银矿床成矿时代等资料都表明长坑金矿赋金硅质岩不是简单热水沉积或热液蚀变作用形成的,而是多次硅化作用的产物,至少经历了热水沉积硅化、成岩硅化、金矿成矿热液蚀变硅化及银矿成矿热液蚀变硅化作用的叠加。热水沉积硅质岩形成富金矿源层,为成矿提供了物质基础。

The Changkeng gold-hosting siliceous rock occurs in the contact zone between the Lower Carboniferous Zimenqiao Group bioclastic limestone and the Upper Triassic carbonaceous argillite or the Lower Carboniferous Zimenqiao Formation sihstone, with a thickness ranging from 1 to 50 m. The siliceous rock consists mainly of thin-bedded and laminated, massive and brecciated cherts. The Changkeng gold ore occurs mainly in the breccias and less in the siliceous rock and is characterized by disseminated mineralization. The evidences in hand such as the siliceous rocks having thin-bedded and laminated structure, a number of radiolarians found in the laminated and massive cherts, detritus paralleling to siliceous interacted beds in breccias, massive siliceous rocks containing framboidal pyrite, together with the reported ages of the Changkeng gold and the Fuwan silver mineralization that associated with strong decarbonification and silicification, suggest that the Changkeng gold-hosting siliceous rock owes its origin to multistage silicification, including at least syngenetic, diagenetic, hydrothermal silicification associated with gold mineralization and silver mineralization, respectively. The syngenetic chert with high background gold content favors the Changkeng gold mineralization in the brecciated chert.