不整合面控制内生金属成矿的新实例:山东沂南金铜铁矿床

山东沂南矽卡岩—热液型金铜铁矿床产于燕山期中酸性杂岩体的接触带及其外侧围岩中。近年来,在太古宇与新元古界之间不整合面及其上覆的新元古界地层中新发现了两层矿体,同时在不整合面以下局部地段的太古宇花岗片麻岩中也见有金铜矿化。受控于不整合面的矿体多呈层状、似层状,埋藏深度大(一般介于430~650 m),产状平缓,侧向延伸连续且稳定。作为一种容易失稳的构造薄弱带,不整合面及其上下机械性质不同的岩层之间极易产生层间破碎、滑脱,导致岩浆及其所分泌的含矿气水热液顺层贯入,并通过交代—充填作用成矿。同时,不整合面又是一个地球化学性质的转换带或地球化学屏障,盖层(含砾砂岩、砂岩、页岩夹泥灰岩)与基底岩石(花岗片麻岩、斜长角闪岩)化学成分和性质的显著差异,也是控制不整合面成矿的重要因素之一。不整合面以下太古宇花岗片麻岩中细脉浸染状金铜矿化,则可能与沿不整合面的拆离断裂活动引发的基底张性裂隙有关。该矿床中不整合面附近矿体的发现,对矿山深部、外围乃至整个鲁西地区的成矿规律研究和找矿勘探工作,具有重要的理论和实际意义。

A New Example of Unconformity-Related Endogenic Metallization:the Yinan Au-Cu-Fe Deposit in Shandong Province, China

The Yinan skarn and hydrothermal type Au-Cu-Fe deposit in Shandong Province occurs in the contact zone of the intermediate-acidic composite intrusions of the Yanshanian age and their surrounding wall rocks.In the recent years,two new ore layers have been discovered on the unconformity surface between the Archean and Neoproterozoic as well as in the overlying Neoproterozoic cover rocks.Locally in the Archean basement rocks below the unconformity,Au and Cu mineralization has also been observed.The unconformity-controlled orebodies are typically layer-or sheet-like and laterally continuous and flat,with a normal depth of 430-650 m beneath the surface.Tectonically as an unstable and weak zone,the unconformity surface and the overlying interfaces between mechanically different strata are ready to be fractured and glided during later tectonic activity and magmatic intrusion,thus resulting in the filling and mineralization of magmas and related hydrothermal fluids.Meanwhile,the unconformity surface is usually served as a geochemical barrier,and the marked difference in chemical composition between the cover rocks(pebbled sandstone,sandstone and shale interbedded with argillaceous limestone) and the basement rocks(granite gneiss and amphibolite) may also have played an important role in the unconformity mineralization.The veinlet and disseminated Au and Cu mineralization in the Archean basement rocks may be related to the extensional cleavages in the basement caused by the detachment of the unconformity surface.The discovery of the unconformity related mineralization in the Yinan deposit is of great significance to the study of metallogenesis and exploration both in the mine and in the entire western Shandong Province.