长江中下游成矿带宣城矿集区重磁场特征与找矿启示

Gravity and magnetic characteristics of Xuancheng ore concentration area along Middle-Lower Yangtze River Valley metallogenic belt:Implications to ore prospecting

宣城矿集区位于长江中下游成矿带东段的安徽省南陵-宣城盆地,是长江中下游成矿带新一轮找矿工作的重点勘查区。为查明成矿深部背景,发掘成矿潜力,亟待了解深部结构特征。本文使用地面测量1∶25000重力和1∶10000磁力数据,通过重磁场分离和密度、磁化强度三维反演,结合岩矿石的密度、磁化率等物性测量结果,以及区域地质和矿床资料,以期揭示深部构造及与成矿关系。研究结果表明,新河庄背斜、陈家湾向斜、马山埠背斜和昆山向斜等褶皱构造横向上剩余密度正负差异显著呈相间分布的深部特征,垂向上褶皱构造的最大深度约为2 km;在褶皱构造下方分布北西浅、往南东逐渐加深的低密度、低磁性层,推测可能为研究区内茅山-九连山推覆构造的滑脱面。马山埠背斜轴部花岗闪长斑岩附近的重高磁高组合异常是铜山-荞麦山矽卡岩型矿床的找矿线索,然而成矿岩体规模较小,深部磁化强度弱,马山埠背斜附近深部找矿潜力有限。茶亭矿区呈重高磁高组合异常特征,同时成矿的石英闪长玢岩岩体与围岩灰岩、上覆火山岩磁性差异明显,这些特征是重要的找矿线索。文章研究结果证实,茶亭下方-400^-1900 m磁化强度正异常区域对应茶亭铜金矿床,这为在研究区其他地点深部进一步寻找斑岩型、隐爆角砾岩型铜金矿床提供了地球物理依据。

The Xuancheng ore concentration area,located in the Nanling-Xuancheng Basin in Anhui Province in eastern of the Middle-Lower Yangtze River Valley metallogenic belt,is one of the key exploration areas in this belt.In order to find out the background and potential of mineralization,it is necessary to study the characteristics of deep structure of this region.Based on the 1∶25000 ground gravity and 1∶10000 ground magnetic data as well as gravity and magnetic field separation and density,magnetization three-dimensional inversion,and regional geology,the authors tried to reveal the inner relationship between the deep structure and mineralization.The results show that positive and negative differences of residual density of the anticlines such as Xinhezhuang,Chenjiawan,Mashanbu andKunshan in this region are significant,with features of alternative distribution in horizontal direction and the maximum depth of Ca.2 km in vertical direction.The low-density and low-magnetic layer,which is distributed under the fold structure,is characterized by shallowing in the northwest and gradually deepeneing in the southeast,indicating that it may be the slip surface of Maoshan-Jiulianshan nappe structure in the study area.The high magnetism and high weight anomaly near the granodiorite porphyry in the axis of the Mashanbu anticline is a prospecting clue for the Tongshan-Qiaomaishan skarn deposit;however,the small scale ore-forming pluton and the weak magnetic intensity indicate a limited ore prospecting potential in this area.Together with the obvious magnetic differences between quartz-diorite porphyrite and surrounding limestone and the overlying volcanic rocks in the Chating mining area,the high magnetism and weight anomaly feature seems to be an important prospecting clue.It is proved that the top and edge of the positive magnetic intensity anomaly area from-400 m to-1900 m correspond to the Chating Cu-Au deposit,which will provide geophysical basis in search for porphyry,cryptoexplosive breccia and hydrothermal lead-zinc deposits in other regions.