摘要
本文通过对红花沟金矿铅、硫、氧、氢等稳定同位素研究,及微量金、铅、铀、稀土元素的研究指出,成矿物质主要来源于太古代变质岩及其重熔产物,成矿溶液主要来源于大气降水;强调了大气降水在成矿物质迁移、富集过程中的作用。建立了矿源层、构造、热源三位一体的成矿模式。
The Honghuasou gold deposit is located within the Yunwushan uplift on the northern flank of the Inner Mongolian anteclise and also lies at the intersection of the Chifeng-Chaoyang structural belt with the Chifeng-Longhua structural belt. Archeozoic amphibolite, amphibolite gneiss and various sorts of migmatite crop out in the orefield, and Upper Jurassic volcanic rocks are distributed extensively. Magmatic rocks are not widely developed, and are dominated by intermediate-acid dykes, of which the pre-ore diorite porphyrite is intimately related to mineralization.Orebodies (occurrences) are mostly distributed in Archeozoic metamorphic rooks and controlled by NNW-SN trending faults, belonging to gohi-beariug quartz vein type deposit. Metallic minerals are mainly pyrite with small amounts of chalcopyrite and galena. Ore grade is closely associated with contents of sulfides. Archeozoic amphibolitic metamorphic rocks contain abundant gold (10.7ppb). The pre-ore diorite porphyrite also contains rather high gold(6.4 ppb) REE pattern suggests that it was formed as a result of partial(10% )melting of amphibolitic metamorphic rocks.The ores contain quite low radiogenic lead, and the single stage model ages are old (within the range of 1700-1800 Ma), indicating that lead was derived from an uranium-deficient area and characterized by multi-stage evolution. The whole rock lead isotope composition of the granite porphyry on the southern side of the ore district is quite similar to the ore lead, and the granite porphyry was formed by remelting of Archeozoic amphibolite. Amphibolite is poor in uranium (0.24ppm), rich in gold and exhibits multistage evolutionary history; in addition, gold in amphibolite is most readily extracted and activated by hydrothermal fluids. It is therefore conceivable that amphibolite and its remelting products might have been the parent rock of lead and the initial source bed of gold.
Sulfur isotope composition is rather uniform in the ore deposit, and the overwhelming majority of samples are within the narrow limits of 3.5-4.5‰, suggesting the unity of sulfur source and the stability of physicochemical conditions. Whole rock δ^(34)S values of amphibole and pre-ore diorite porphyrite are respectively 2.9 and 3.1‰, which are fairly consistent and within the distribution range of δ^(34)S values of the ore eposit, implying their sanguinity and their genetic connection with the ore sulfur. δ^(34)S values of pyrite in the ore veins gradually increase from the depth upwards, but tend to decrease progressively in the middle.δ^(18)O values of quartz in ore veins vary insignificantly, mostly within, the range of 11.5-12.5‰; vertically, δ^(18)O values of quartz and δ^(31)S values of pyrite show similar variation regularity。 δ^(18)O values of ore fluids are in the range of 0.8-5.9‰, distant from the δ^(18)O ranges of magmatic water and metamorphic water but close to the δ^(18)O range of meteoric water. δD values of quartz inclusions also exhibit characteristics of meteoric water(-85.5-109.7‰). Calculation shows that ore fluids were formed through hydrogen-oxygen isotope exchange between the initial meteoric water(δ1)=-96‰, δ^(18)O=-23‰) and the pre-ore diorite porphyrite and amphibolite at 200-250℃, with the ratio of water/rock being 0.3 or so.The vertical variations in δ^(34)S values of pyrite in ore veins and δ^(18)O values of quartz must have resulted from the upward decrease in ore-forming temperature, the unceasing addition of fresh meteoric water, the progressive rising of fO_2 values and the remarkable decrcase in δ^(34)S and δ^(18)O walues of the whole system due to the appearance of SO_4^(2-) in the upper part of the ore veins.
出处
《矿床地质》
CAS
CSCD
北大核心
1990年第3期257-269,共13页
Mineral Deposits
