鲁中南地区第四系河流砂金成矿特征的研究

RESEARCHES IN MINERALIZATION CHARACTERISTICS OF QUATERNARY PLACER GOLD DEPOSITS FROM RIVERS IN THE SOUTH OF CENTRAL SHANDONG PROVINCE

本文研究了鲁中南地区河流砂金富集成矿特征及成矿时代.区内第四系出露时代齐全,成因类型繁多,岩性复杂.河流砂金矿层主要位于冲积或冲洪(洪冲)积物的底部,即古老变质岩系基岩面之上的含泥砂砾或砾砂等粗粒沉积物中.据资料和第四纪以来气候的冷暖变化,区内河流砂金的成矿时代可划分为中更新世(早期)、晚更新世(早期)和全新世(早、中期).

Quaternary sediments from Pleistocene to Holocene are all exposed in the south of central Shandong Province, but late Pleistocene and Holocene sediments are of the widest distribution and cover a relatively large extent. They can be seen in coastal plain, hilly area, intermontane basin, valley and both banks of a river. They have complicated lithological forms and various original types, inclucling alluvial, diluvial-alluvial (alluvial-diluvial), diluvial, marine, lake, swamp, eluvial, slope wash and eluvial-slope wash origins, of which alluvial, diluvial-alluvial or alluvial-diluvial sediments are closely related to mineralization of fluvial placer gold. Fluvial placer gold deposit is usually located in gravelly sands, sandy gr-avels or coarse sand and gravel bed (generally 0.5-3.0m thick) over basero-ck surface in river beds, valley flats or fluvial terraces. Content of gravels in gold-hearing sediments increases relatively from up to down and so does the gravel diameter. And gold tenor also has a tendency of increase. The gold-bearing beds are overlain by fine-grain sediments such as sand, secon-dary sand soil or secondary clay. Sediment in placer gold bed is dominated by sand or gravel. There is only a little amount of mud in it. The average content of gravel makes up 32.52%, varying between 10.00 and 59.83%. Gravel is generally very fine. Boulder is only sparsely scattered. Both sorting and roundness are very poor. Gravel compositions are mainly metamorphic and intrusive rocks. Sand has an average content of 54.49%, dominated by coarse sands, mainly quartz and feldspar, with good roundness and poor sorting. Average mud content is 17.31%. When mud content increases relatively in placer gold bed, gold tenor also increases correspondingly. There are various species of heavy minerals (38 species) in the placer gold bed, with complicated assemblages and high content. According to investigation and data analysis, mineralization period of the fluvial placer gold can be divided into early middle Pleistocene, early late Pleistocene and early and middle Holocene. Fluvial placer gold deposit of early Pleistocene has uot been found yet. It is may be due to study limitati-on or destruction during the too long formation process.