右江裂谷区三叠系岩石物性特征及其与金矿化的关系

PHYSICAL CHARACTERISTICS OF TRIASSIC SEDIMENTARY ROCKS AND THEIR RELATIONS TO GOLD MINERALIZATION IN YOUJIANG RIFT ZONE

本文阐述了右江裂谷区微细粒浸染型金矿床控矿层位三叠系百蓬组泥质粉砂岩及砂质泥岩的粒度，比表面、孔隙度及孔隙类型和渗透率等物性特征，讨论了与其成矿流体的循回、水岩反应及其有效浸取围岩矿物质的关系。在此基础上提出了成矿流体和成矿物质主要来自于地层；由于热液向低势能方向迁移，造成断裂发育的盆地边缘区和水下隆起周围的环状断裂带为金矿床沉淀的场所。并通过形成金矿所需热液量的估算得出，该区金矿床的形成，是由于热流体（发生在矿区及其外围）的深循环作用或者是流体多次循回叠加作用。

This paper studies grain size, specific surface, porosity, pore type and permeability of pelitic siltstones and sandy mudstones of Triassic Baipeng Group which control the distribution of fine grained disseminated type gold deposits in Youjiang rift zone, and also discusses their relations to the circulation of ore forming fluids, the interactions between the fluids and sedimentary rocks in the Baipeng Group, and the gold mineralization. The pelitic siltstones and sandy mudstones have bigger specific surface, porosity and permeability and better continuous interstice, which play a key role in the extensive circulation of the ore forming fluids, the interactions between the fluids and the sedimentary rocks, and the migration of gold. The ore forming fluids and gold came from the Triassic sedimentary rocks. The ore forming fluids derived from the pore water and the absorbed water liberated during the dehydration process of the sedimentary rocks and the formation water sealed in the strata circulate extensively owing to the action of pressure and thermal gradient. The gold in the strata is extracted through interactions between the fluids and the strata, migrates in the form of HS - Au complex or gold organic complex, and precipitates in the decompression zone. Therefore, the margin of a basin with well developed faults and the peripheral ring faults of the underwater uprift are favorable places for gold deposition. Calculation of fluid amounts for the formation of gold deposits in Jinya and Gaolong gold ore districts indicates that water quantities in the sedimentary rocks within the limits of gold districts are much lower than those required for transportation of gold in the deposits, suggesting that the ore forming fluids have probably undergone extensive circulation beyong the gold ore districts.