扬子地台西缘大渡河谷超大型层状铅锌矿床地质地球化学特征及成因

20世纪90年代以来，四川地矿局207地质队及地方采矿业在扬子地台西缘大渡河谷沿岸，相继发现了黑区—雪区、红花、白熊沟、核桃坪、养善坪—中溪坪—宝水溪—双凤沟等层状铅锌矿床及矿点。其中，黑区—雪区矿床的矿体地表露头长达6000m，估算的铅锌资源量达370万吨，达到超大型矿床的规模。不同的矿床、矿点的分布构成了长度大于50km的铅锌矿化带，预测铅锌资源量有望达1000万吨以上。各矿床、矿点产于上震旦统—下寒武统灯影组顶部麦地坪段含磷硅质白云岩的相同层位，矿化与硅质岩及角砾状白云岩层关系密切。矿床中发育层状、纹层状、条带状、同沉积角砾状、层间揉皱等构造，沉积特征明显。矿床的地质、地球化学特征显著区别于区域上以往发现的产于地台盖层碳酸盐岩中具有明显后生成因特点的密西西比河谷型（MVT型）铅锌矿床，也有别于产于中元古界褶皱基底中的火山沉积块状硫化物型（VMS型）铅锌矿床。笔者的研究表明，与铅锌矿密切共生的硅质岩为典型的海底热水沉积产物，铅锌矿床属于海底喷流—沉积成因（SEDEX型）；成矿作用受晚震旦世—早寒武世北东东向延伸的汉源—峨眉凹陷及同生断裂带的控制。该类层状铅锌矿床可能是扬子地台西缘铅锌矿聚区中最具找矿潜力的矿床类型。

Geological and Geochemical Characteristics and Genesis of Supper-large-scale Sedex-type Stratiform Lead-Zinc Deposits in the Dadu River Valley on the Western Margin of the Yangtze Craton

A number of conformable stratiform Pb-Zn deposits and occurrences such as Heiqu-Xuequ, Honghua,Baixionggou, Hetaoping, Zhongxiping, Baoshuixi and Shuangfenggou have been discovered since the 1990s along the Dadu River valley on western margin of the Yangtze Craton by the 207 Geological Team under the Sichuan Geological and Mineral Resources Bureau and local mining companies. These Pb-Zn deposits and occurrences are hosted in the same stratohorizon of phosphate and siliceous dolomite of the Maidiping Member on the top of the Upper Sinian-Lower Cambrian Dengying Formation and the ore beds are confined to the siliceous rock and brecciated dolomite layer. The outcrop of the ore beds of the Heiqu-Xuequ deposit has a length of 6000m, and its Pb-Zn resources is estimated up to 3.7 Mt. The distribution of various deposits and occurrences forms an ore belt over 50 km long and the total Pb-Zn resources in the ore belt is hopeful up to 10 Mt. The typical ore structures, e.g., stratiform, laminated, banded, sedimentary brecciated, interbedded folded, and slump structures, exhibit sedimentary characteristics. The geological and geochemical characteristics of these stratiform deposits are notably different from those of both the MVT-type Pb-Zn deposits hosted in the cover carbonate rocks and VMS-type Pb-Zn deposits hosted in the Mesoproterozoic metamorphic basement rocks of the Huili Group in the regional Pb-Zn ore belt. This study suggests that the silicalite paragenetically related to Pb-Zn ore is originated from hydrothermal sedimentation, and the deposits are genetically Sedex-type. The Pb-Zn mineralization is controlled by the Hanyuan-Emei depression and a contemporaneous fault in the middle of the depression during the Late Sinian-Early Cambrian Dengying Period. The Sedex-type deposit is probably the one with largest resources potential in the Pb-Zn belt on western margin of the Yangtze Craton.