桂北摩天岭西段高堤地区脆韧性变形特征与铀成矿关系

Brittle-ductile Deformation Dominated Uranium Mineralization in the Gaodi Area of the Western Motianling Dome,Northern Guangxi

桂北摩天岭位于江南造山带西南端,是九万大山-元宝山铀成矿区的重要组成部分。高堤铀矿点位于摩天岭西段,矿区内脆韧性变形发育,铀成矿潜力较大,但是脆韧性变形与铀成矿的关系不清晰,限制了区内找矿方向。本次研究对高堤地区进行野外构造特征识别与室内微观构造研究,发现区内麻木岭和梓山坪脆韧性剪切带走向NNE、倾向NW,发育长石旋转碎斑、云母鱼、S-C组构及书斜构造等,指示麻木岭和梓山坪脆韧性剪切带具左旋逆冲特征。区内早期发育的韧性剪切变形为先存构造,后叠加逆冲断层,同时在麻木岭剪切带上盘发生反冲断层,导致麻木岭剪切带以西花岗岩内发育的片麻理倾向SE,麻木岭剪切带以东片麻理倾向NW,及麻木岭剪切带上盘与其近平行的韧性剪切带产状倾向发生反转。结合铀矿体产出特征分析,认为麻木岭和梓山坪剪切带作为导矿构造,与深部沟通良好,其自身成矿空间有限、潜力较小;麻木岭剪切带上盘叠加的逆冲断层F_(1)、F_(2)和梓山坪剪切带旁侧韧性剪切带属配矿构造;F_(1)、F_(2)逆冲断层夹持区透镜体发育的裂隙系统和梓山坪剪切带旁侧糜棱岩面理构造为储矿构造。在此基础上,建立了高堤铀矿构造控矿模式,提出在高堤地区(即高堤屯)南东侧发育的麻木岭剪切带上盘断裂构造,即走向NNE、倾向SE的断裂破碎带是区内重要的找矿方向。

The Motianling dome,at the southwest end of the Jiangnan orogenic belt in Northern Guangxi,is an important segment of the Jiuwandashan-Yuanbaoshan uranium metallogenic region.The Gaodi uranium deposit is located in the western part of the Motianling dome,where brittle-ductile deformation is well developed.However,the relationship between brittle-ductile deformation and uranium mineralization is not clear,which hinders ore prospecting in the Gaodi region.This paper presents the structural characteristics of the fault,the field and microstructures of mylonites,discusses the regional deformation history,and proposes a new direction for regional uranium ore exploration.Both the NNE-trending Mamuling(Fm)and Zishanping(Fz)faults are NW-dipping with well-developed rotating debris of feldspar,mica fish,S-C fabric,and an oblique structure,indicating that the Fm and Fz faults experienced left-lateral thrusting movement.Field observations showed that the Fm and Fz faults probably were the early-formed ductile shear zones,which were superimposed by the later thrusting movement.The thrusting of the faults in the hanging wall of Fm probably led to the formation of the genessic texture of the granite,which dips to the SE in the west side and NW in the east side of Fm,and the overturned occurrence of the ductile shear zone near the upper wall of Fm.Fm and Fz probably were ore-conducting structures;however,the mineralization potential of these two faults may have been small due to their limited space.The thrust faults F_(1) and F_(2) were superimposed on the hanging wall of Fm;and the ductile shear zone adjacent to Fz probably controlled the migration of the ore-forming materials.The lenslike fissure systems between the F_(1) and F_(2) faults might be the main ore-bearing structures.Finally,a tectonic ore-controlling model of the Gaodi uranium deposit was established.We suggest that the NNE-trending and SE-dipping fault zone and fractures in the hanging wall of Fm on the southeast side of the Gaodi area(Gaoditun)are the most favorable ore-forming areas and should be the targets of future ore prospecting.