暗色岩脉与铀成矿关系研究

A STUDY OF THE RELATIONSHIP BETWEEN THE DARK DYKE AND THE URANIUM MINERALIZATION

本文对暗色岩脉与铀成矿关系在铀成矿的源—运—储三方面进行了较为深入的研究。结果表明,暗色岩脉对铀成矿所起的作用主要是提供有利于铀沉淀富集的场所。岩脉的铀含量数倍于同类岩石是花岗岩地区暗色岩脉的特点,但不代表暗色岩脉能够为铀成矿提供铀源。根据暗色岩脉富含挥发分、所代表的岩浆活动与铀成矿作用最接近、成脉与成矿构造上的关联性以及暗色岩脉是深部岩浆浅部表现形式的成因特点,认为暗色岩脉所代表的岩浆活动、构造运动还可以为铀从花岗岩中的活化转移创造有利条件,岩脉的侵入作用虽然对围岩具有一定的加热作用,但还不能成为铀成矿的主要热源。

Uranium deposits related to dark dykes are rather common and typical in uranium-earing granite of anling region. This sort of deposits belong to mesothermal-epithermal type nd are distinguished from other types y imple mineral assemblage and higher industrial grade. his paper makes a fairly thorough study on the relationship etween the dark dyke and the ranium mineralization in three aspects of the ore-forming process, i.e., source aterials, ransportation and deposition.Studies on uranium content of dark dykes demonstrate that dark ykes from S rea, I area, uranium-bearing granite and uranium-barren granite do not show bvious ifference in uranium content. his fact, combined with metallogenic characters of this type of eposits, leads to the conclution that it was quite mpossible for dark dykes to provide uranium intralization with source materials.Based on the fact that dark dykes re rich in volatiles, hat their magmatic activity is close to uranium mineralization in time, that dykes are ectonically elated to uranium deposits, and that the genetic features of dykes are anifestations of magmatic activity at depth, it s considered that the magmatic activity and ectonic movement represented by dark dykes might have created a avorable condition for obilization and transference of uranium from granite. Though playing some heating role, the vasion of dark dykes could not act as the main heat source for uranium mineralization.Studies how that the major ole played by dark dykes in the process of uranium mineralization seemned o rovide favorable places for the eposition of uranium. The enrichment and precipitation of ranium in dark dykes are mainly attributed to the boundary effect' between the dark dyke and rani te caused by physical-chemical difference between the two sorts of ocks. The etermination long a section shows that ⊿Eh value of dark dykes is much lower than that of granite, i. e., ecreases abruptly from -20mV in granite to -40mV in dark dykes. Considering the existence of uch reducing ases s H_2S, CH_4 and CO in the dykes, the actual ⊿Eh value difference should be uch greater than that observed. It is herefore conceivable that when uranium-bearing ydrothermal fluids passed through dark dykes from granite, the brupt change in physical-hemical condition must have resulted in the reduction of U^(6+) to U^(4+) and caused ranium recipitation and mineralization.