扬子地块北缘观音庵铅锌矿找矿模型及远景预测

西乡观音庵铅锌矿位于扬子地块北缘汉南—碑坝基底隆起的东南缘,属马元铅锌矿带南岸山—松坪铅锌矿东矿段沿倾向自然东延部分。区内地层产状总体东倾,倾角平缓,一般5°~15°,局部受断层或次级穹窿构造影响,具波状起伏特征,震旦系灯影组多处形成＂似构造窗＂。在观音庵沟一带圈定了4条铅锌矿体。铅锌矿体赋存层位为上震旦统灯影组上段第二岩性层,赋矿岩石均为厚层角砾状白云岩,具有层控、岩控的特点;矿体一般呈层状、似层状,顺层或微斜切层理产出,具有膨大狭缩、分枝复合、分段集中等特点。铅锌矿体长300~1440 m,厚度1.18~1.70 m,铅品位1.18%~2.20%,锌品位1.03%~2.32%。研究认为区内铅锌矿成因类型类似于密西西比河谷型（MVT型）铅锌矿,但也有着一定的差异,可称为＂台缘型＂或＂扬子型＂铅锌矿。通过控矿条件分析及找矿模型建立,认为区内深部找矿应沿基底隆起周边向外深部灯影组角砾状白云岩层位,在扬子地块北缘∈1/Z2平行不整合面下10~50 m范围内的破碎角砾状白云岩带;重点区段是角砾岩带延伸方向及灯影组隐伏区。从而预测本区深部找矿前景较大。

ORE-PROSPECTING MODEL AND POTENTIAL PREDICTION OF LEAD-ZINC MINERALIZATION IN GUANYINAN AT THE NORTHERN MARGIN OF THE YANGTZE LAND-MASS

The Guanyinan lead-zinc deposit is located in the southeastern margin of the basement uplift between Hannan and Beiba at the northern margin of the Yangtze land-mass,belonging to the east extension along the dip direction of the east ore blocks of the Nananshan-Dongping lead-zinc deposit in the Mayuan lead-zinc ore zone.The attitude of stratum in this area is mostly dip to east with a gentle slope,generally between 5° and 15°,which was locally effected by faults and/or secondary domal structure with undulation features,forming some similar tectonic windows in the Sinian Dengying Formation.There are four lead-zinc ore bodies delineated in the Guanyinan area.The four orebodies occur in the second lithostrome at the upper Dengying Formation of the Sinian system and the host rocks are generally thick-bedded brecciated dolomite with features of stratabound and lithologic control.Ore bodies in this area are generally in appearance of bedded and stratoid structures and distributed along beddings or slightly inclined beddings,characterized by inflation and pinch,bifurcation and recombination,and accumulation in blocks.Lead-zinc ore bodies have a length ranging between 300m and 1,440m,thickness between 1.18m and 1.70m,lead grade between 1.18% and 2.20%,zinc grade between 1.03% and 2.32%.The genetic type of the lead-zinc deposit in this area is similar to Mississippi valley type（MVT）with some differences.So,it could also be attributed into the type of platform margin or the Yangtze type.Based on analysis of ore-controlled conditions and creation of ore-prospecting model,it is suggested that ore-prospecting at depth in this area should be commenced along the uplift margin of basement to the outward brecciated dolomite horizon of the Dengying Formation at depth,the fractured and brecciated dolomite zone within a range between 10m and 50m under the parallel unconformity of ∈1/Z2 at the north margin of the Yangtze land-mass,in which the blind range in the Dengying Formation along the brecciate zone is the focal places and a great potential for ore-prospecting is in a deep part.