南岭及其邻区几个区域地质矿产问题的探讨

PROBLEMS ON THE REGIONAL GEOLOGY AND MINERAL RESOURCES IN NANLING AND ITS NEIGHBOURING AREAS

本文对南岭及其邻区几个地质矿产问题进行了探讨,并提出一些看法:如认为前寒武系可划分为三个系;该地层是金、锡的矿源,是南岭地区、金、锡矿质的主要来源;元古代的蛇绿岩、根据其特征是形成于边缘海的拉张带或深大断裂带,是原生侵位的;现所认为和锡矿有关的雪峰期花岗岩体,有可能是以四堡期为主的多期复式岩体;一次强烈的构造运动所影响的范围,是由当时沉积海盆的边缘至中心逐渐减弱,形成了上下地层接触关系为不整合—假整合—整合。

1. The unified stratigraphic classification and division of the Precambrian and the main ore prospects According to the present data available, the Precambrian in the Nanjing region may be divided in descending order into the Sinian (600—800Ma), the Qingbaikou System (800—1000Ma) and the Jixian Sytem-Chan-gcheng System (>1000—1800Ma). In this sequence of strata, not only very rich mineral resources have been identified but much potential of mineral prospecting also exist. It is a very good source bed and an important source of ore substances in the region. So to strengthen its study is of major stratigraphic significance. 2. Characteristics of Proterozoic ophiolites and their environment of formation Three suites of ophiolites have been found in the region, and occur in the Jixian System-Changcheng System, the Qingbaikou System and the Sinian respectively. From northwest to southeast they are distributed regularly from older to younger. They extend from northeast to northeast-east, parallelly to the strike of the strata where they are localized, and are folded synchronously with the strata. According to their modes of occurrence, they were formed in an extension zone or a deep fracture zone similar to the modern marginal sea of the Western Pacific type rather than in the mid-ocean ridge. They originated by primary emplacement rather than by secondary tectonic emplacement. 3. The age of continental crust anatectic granite and its related metallogenic epoch It is considered now that the oldest continental crust anatectic granite and its related metallogenic epoch are the Xuefeng period (700—800Ma). But as the Sibao movement was stronger than the Xuefeng movement and there are gravels of tourmalite containing Sn 0.38％ in the basal conglomerates of the Qingbaikou System, there should exist the continental crust anatectic granite of the Sibao period (>1000Ma) and its related metallogenic epoch. The Xuefeng-aged massif considered now might be a polyphase composite massif. 4. The areal extent of influence of a strong tectonic movement According to the actual data in the Nanling region, a strong tectonic movement usually can only generate folds in the strata on the margins of a sedimentary basin, while the central part of the basin continued to receive sediments. Therefore, the contact relationships of the strata are uuconformity-disconformity-conformity respectively from the margins of a basin to its central part. Whether such an inherited basin is more favourable to ore (oil)formation merits a deep-going study.