摘要
本文对中国东南部萤石矿床,根据野外地质和锶、氢、氧同位素,REE地球化学等研究以及成矿年龄测定,建立了晚白垩世地热水环流汲取成矿模式,并划分为深循环淋滤汲取和浅循环淋滤汲取两种机制。中生代火山岩区的萤石成矿主要与前者有关,成矿物质主要来自赋矿岩石下伏基底的前寒武纪变质岩;燕山期花岗岩区的萤石成矿则以后者为主,威矿物质主要来自赋矿岩石(花岗岩及沉积岩)。
The flourite deposits of southeastern China mainly belong to vein-type deposits with quartz-flourite formation. Judging by the spatial relationship between the deposits and magmatic rocks, these flourite deposits may be divided into two types (Ⅰ and Ⅱ) occurring respectively in Mesozoic volcanic rock areas, and in Yanshanian granite areas.
The present study has revealed the following facts:
1) The two types of flourite deposits have the same age with respect to their mineralization (70—90 Ma). Wherever they occur, either in volcanic rocks or in granites, the age of flourite mineralization always lags behind by 40—70 Ma than that of the host rocks.
2) The two types of flourite deposits show the similar wall rock alteration, mineral association and ore-forming temperature (100—200~C).
3) The ore-forming fluids of both types belong to geothermal waters derived from die meteoric waters of Late Cretaceous age. The only difference lies in that the water-rock ratios (0.05—1.5) of the hydrothermal system related to type Ⅰ are lower than those (generally morethan 1.5) of the hydrothermal system related to type Ⅱ.
4) Early-stage (main mineralization stage) flourites from type Ⅰ have ^(87)Sr/^(86)Sr ratios ranging from 0.7306 to 0.7710. Most of these flourite ^(87)Sr/^(86)Sr ratios are in the range (0.7454—0.9090) of underlying Ptecambrian metamorphic rocks at the time of mineralization (～80 Ma), but they differ significantly from those (0.7085—0.7298) of the host rocks at the mineralization time. Only late-stage flourites and calcites from type-Ⅰ have ^(87)Sr/^(86)Sr ratios similar to those of the host rocks at this time. However, for type-Ⅱ, the ^(87)Sr/^(86)Sr ratios (respectively, 0.7094—0.7166 and 0.7099—0.7188) of early flourites or late flourites and barites fall into the range (0.7059—0.7276) of the host rocks of type-Ⅱ at the time of mineralization (～80 Ma).
On the basis of the above-mentioned data, combined with field geologic and REE geochemical investigations, for the two types of fluorite deposits, the authors suggest a minerogenetic model of circulation and drawing of Late Cretaceous geothermal waters. The model in cludes two mechanisms: (1) the leaching-out and drawing through deep circulation of the geothermal water, and (2) the leaching-out and drawing through shallow circulation of the geothermal waters. Deposits of type Ⅰ are mainly related to the former mechanism and ore substances were mainly derived from the Precambrian metamorphic rocks underlying the host rocks, while deposits of type Ⅱ are mainly related to the latter mechanism and ore substances were mainly derived from host rocks (granite and/or sedimentary rocks).
出处
《地质学报》
EI
CAS
CSCD
北大核心
1991年第3期263-274,共12页
Acta Geologica Sinica
