南襄盆地泌阳凹陷含碱建造成因及找矿思考

南襄盆地泌阳凹陷不仅蕴藏着丰富的石油天然气资源,而且还赋存有目前亚洲第一、世界第三大天然碱矿床。通过对已有地质、地球物理资料的综合分析,研究了形成碱矿所需的巨量物质来源以及盐(碱)矿、油气资源共生问题,讨论了含碱建造的形成背景及成因,分析了泌阳凹陷天然碱、石油天然气与邻区桐柏矿集区金属矿床之间可能的成因联系。研究表明:南襄盆地是形成在特殊地质背景上的构造断陷盆地,深部软流圈地幔异常凸起,盆地内深大断裂发育。泌阳凹陷的含碱建造中发现大量的热液矿物和幔源物质,其组分特征显示深部幔源热流体活动强烈。整个含碱建造包括白云岩、盐(碱)、油气(或油页岩)的成矿物质主要来自幔源烃碱流体,是幔源烃碱流体经盆地内深大断裂向上运移进入盆地形成的,盆地深部应该有基岩油气藏。泌阳凹陷含碱建造中的油气、盐碱矿与桐柏矿集区金属矿产可能是在同一个完整的幔源流体成矿系统中形成的。

Background and Genesis of Alkali Bearing Formation in Biyang Sag,Nanxiang Basin

Biyang Sag in Nanxiang Basin is rich in oil and gas resources,and contains the largest natural alkali deposit inAsia,which is also the third largest in the world. In this paper,the problems in the huge material source required for the formation of alkali deposit and the symbiosis of salt(alkali) ore and oil and gas resources are studied through comprehensive geological and geophysical analysis,and the background and genesis of alkali bearing formation,the possible genetic relationship between natural alkali,oil and gas and metal deposits in the adjacent Tongbai ore concentration area are discussed. The resultshows that the Nanxiang Basin is a tectonic faulted basin formed on a special geological background with abnormal uplift ofdeep asthenosphere mantle and development of deep faults in the basin. A large number of hydrothermal minerals and mantlederived materials are found in the alkali bearing formation of Biyang Sag,and their component characteristics show strong deepthermal fluid activity. The main ore-forming materials of the whole alkali bearing formation,including dolomite,salt ( alkali),oil and gas (or oil shale),are mainly derived from mantle-derived hydrocarbon alkali fluids,and the upward migration of thesefluids into the basin through regional deep faults results in mineralization. There should be bedrock oil and gas reservoirs in thedeep part of the basin. The oil and gas,salt and alkali in the alkali bearing formation of Biyang Sag and the metal minerals ofTongbai ore concentration area may be formed in the same complete mantle-derived fluid metallogenic system.