凡口铅锌矿床矿石退火结构研究

A STUDY OF ANNEALING TEXTURE OF ORES IN THE FANKOU LEAD-ZINC DEPOSIT

矿石退火结构常见于具有多期成矿特点的硫化物多金属矿床,早期矿石受后来构造-热事件作用而升温,在封闭-半封闭状态缓慢冷却,形成特殊的矿石结构——退火结构。燕山晚期(白垩纪)强烈的构造与岩浆活动,在凡口矿区范围内形成温度大于200℃的热事件(100×10~6a±),由于碳泥质碳酸盐岩围岩的屏蔽,造成缓慢冷却的退火环境,产生球状闪锌矿和{210}、{111}黄铁矿等退火重结晶产物。早期贫矿石经退火作用后,锌铅组分再次富集,矿石矿物颗粒度增大,扩大矿床规模并提高矿石品位和可选性。研究凡口矿床矿石退火结构,有助于了解超大型矿床的特殊成矿环境,并指导找矿勘探。

The annealing texture of ores is frequently observed in polymetallic Sulfide deposits characterized by multiphase ore-forming process. The early ore was heated under the influence of late structural-thermal event and then gradually cooled in an enclosed to semi-enclosed environment, forming a special ore texture——annealing texture. The spherical sphalerite and the pentagonal-dodecahedral and octahedral pyrite in the Fankou lead-zinc deposit are all products of annealing recrystallization. The annealed ore composed of spherical and fine-grained pyrite and quartz, after being fumigated and eroded by aqua regia, exhibits annealing twin crystals of sphalerite. In the late period of Yanshanian orogeny, intense tectonism and large-scale granitic magmatism gave rise to a thermal event with a paleotemperature of some 220℃ in the Fankou ore district. Due to the adiabatic shielding action of the overlying carbonaceous-argillaceous limestone bed, the metallogenic materials in the ore-forming rocks were long in a high-energy and annealing environment and hence underwent large-scale mobilization, migration and enrichment, eventually forming the Fankou gigantic lead-zinc deposit. After annealing, the early-formed lean lead-zinc ore might be converted to rich ore, and the grains of lead and zinc minerals might grow in size through recrystallization, thus raising the washability of ores and the utilization ratio of ore resources. The study of annealing texture of ores helps to understand the physicochemical environment for the formation of ore deposits and guides the ore-prospecting work.