安徽沙溪铜矿区域重磁三维反演与找矿启示

Prospecting Indicator of Anhui Shaxi Porphyry Copper Deposit Based on Regional Gravity and Magnetic 3DInversion

安徽省沙溪铜矿是长江中下游成矿带中最为典型的中生代斑岩型铜(金)矿床,为进一步扩大矿床规模,探索新的找矿靶区,需要开展成矿背景研究,以了解控矿因素和成矿规律,为找矿预测提供基础信息。沙溪铜矿主要赋存在石英闪长斑岩中,了解该岩体的三维空间分布是实现找矿突破的关键环节。本文以重磁三维反演为基础,在沙溪矿区尝试了岩性识别,成功的刻画了含矿石英闪长玢岩、黑云母二长岩、石英闪长斑岩和闪长岩等4类主要岩体的三维形态,并推测了隐伏火山机构的存在。结合大地电磁资料分析,认为沙溪杂岩体形成与西侧的深大断裂关系更密切,与庐枞盆地形成无直接关系,同时也说明沙溪斑岩铜矿与庐枞玢岩铁矿并非同一成矿体系。沙溪铜矿中铜矿体本身不能产生强的重力和磁力异常,但重磁资料可以提供岩体分布信息,地表的弱磁低重力组合、三维重磁反演中的高密度体边上的低磁性体是寻找沙溪铜金矿的有利地段,从而实现间接找矿。综合音频大地电磁探测和重磁三维反演结果分析,认为沙溪主矿带凤台山东侧的沙湖山和夏家墩及凤台山西侧深部是寻找该类型斑岩型铜金矿的有利地段。

Shaxiporphyry copper-gold deposit located in Lujiang county where named as Luzong （Lujiang-Zongyang）ore concentrate district,Anhui province,east China.This deposit is the most typical Mesozoic porphyry copper-gold deposit in the middle and lower reaches of Yangtze River.In order to expand scale of the deposit,it ’s necessary to research metallogenic background to understand ore-control factor and metallogenic characteristics,and then provide basical information for mineral exploration.Quartz diorite porphyry is the main ore bearing pluton in Shaxi deposit,so mapping the three-dimensional space distribution of the pluton is a key step for prospecting.Based on the 3D inversion of gravity and magnetic, we tried the lithology recognition and successfully portrays the three-dimensional morphology of four main types of pluton include ore bearing quartz diorite porphyry,biotite monzonite,quartz diorite porphyry and diorite,and we also speculated a canceled mechanism of the volcano.Analysis with magnetotelluric data,we think the formation of Shaxi intrusion complex have more closely relation with deep fault on its west side,maybe have no direct relation with the formation of Luzong volconic basin.It also proved that Shaxi porphyry copper-gold deposit and Luzong porphyrite iron deposit is not the same metallogenic system.Although copper ore can’t generate stronger gravity and magnetic anomaly,but gravity and magnetic data can provide intrusion information to realize prospecting indirectly.According gravity and magnetic 3D inversion and Audio Magnetotelluric results,we find that ore bearing quartz diorite porphyry can character as low magnetic, low density and high resistivity,so where low magnetic and gravity anomalies in surface,low magnetic body near high density body in 3D inversion model and high resistivity in Audio Magnetoteluric survey are mostly area for mineral exploration.Integrate geophysics exploration and geological interpretation,we believe that the deep part one the west of Shaxi main ore zone,Shahu mountain and Xijiadun which one the east of Fengtai mountain are favorable targets for porphyry copper gold deposit.