铊地球化学和铊超常富集

Thallium Geochemistry and Its Ultra-Normal Enrichment

铊的地球化学性质受其电子构型和地质地球化学作用制约。铊原子处于基态时的电子构型为6S26P1。铊有两个地球化学价态,正一价和正三价,自然界多数呈正一价。铊的电子构型和地球化学性质,使其具有低温成矿、亲硫;高温分散、亲石的双重地球化学性质。在低温高硫还原环境,铊表现出强烈的亲硫性,不仅与汞、锑、砷、铜、铅、锌、铁、金、银等一道参与有色金属和贵金属矿床的成矿作用,而且形成铊的硫化物矿物、铊矿体和铊矿床;在高温低硫环境中,铊表现出明显的亲石性。由于铊的地球化学和结晶化学性质与钾、铷、铯很相近,因此使铊以类质同象形式进入长石、云母、闪石、白云石、迪开石、高岭石等矿物中,导致铊分散。作者尝试性提出,铊超常富集是指其含量普遍达到大于铊成矿的工业品位(n×10-4)或大于铊地壳丰度(0 75×10-6)100倍以上。铊矿区矿物、岩石、土壤、水体、生物和人体中铊含量明显高,且普遍是判别铊超常富集的标志。

The electronic configuration of thallium (Tl) is 6s^26p^1 when Tl atoms are in the ground state. Thallium has two geochemical valent states: Positively monovalent and positively trivalent. It is mostly positively monovalent in nature. The electronic configuration and geochemical properties of Tl make it possess double-edged geochemical properties, i.e., on one hand it is sulpHopHile and can be concentrated to form Tl deposits under low temperature conditions and on the other hand it is lithopHile and is of dispersed occurrence under high temperature conditions. Under Low-temperature, high-sulfur conditions Tl is so strongly sulpHopHile as to take an active part, together with Hg, Sb, As, Cu, Pb, Zn, Fe, Au and Ag, in mineralization of non-ferrous and precious metallic ore deposits, but also in the formation of sulfides of Tl, Tl orebodies and Tl deposits. In Low-temperature sulfide deposits Tl, as a trace element in most case, is incorporated into sulfide minerals such as arsenopyrite, stibnite, realgar, orpiment, pyrite, chalcopyrite, galena and spHalerite. Under high-temperature and low-sulfur conditions Tl is strongly lithopHile in nature. As the geochemical and crystallochemical properties of Tl are closely similar to those of K, Rb and Cs, Tl can be isomorpHously incorporated into feldspar, mica, ampHibole, dolomite, dickite, kaolinite, etc., leading to the dispersion of Tl. Thallium ultra-normal enrichment is Tl-content higher than industrial tenor (n×10^(-4)) or Tl-content 100 times higher than the average crustal content (0.75×10^(-6)). Tl-content of mineral, rock, soil, water, living organisms and human bodies in mining district are remarkably higher than those in the non-mining districts. So they can be used as indicator of ultra-normal enrichment.