一个与铬铁矿富集有关的巨型实验

现在岩石学、矿床学的实验一般用样品是几十毫克、甚至十几毫克,其目的是要精确化。但是许多事实说明,这种精密的实验工作并不能完全解决矿床的成因。要解决矿床成因的问题,至少必须回答下面三个问题:(1)有用金属矿物是在什么条件下形成的;(2)有用金属矿物是如何富集为矿石的;(3)矿石如何具有一定的量,并达到经济上可开采的要求。实验岩石学和实验矿床学的资料一般只说明了第一个问题。

A LARGE SCALE EXPERIMENT ON THE ENRICHMENT OF CHROMITE

A large-scale experiment on the enrichment of chromite was carried out in the course of trial-production of the casting stone from perchromate waste. The melts used for producing the casting stone are composed of perchromate waste, powder coal ash of power station and quartz sand. As a whole it is comparble with the Yoder’s olivine tholeiite in chemical composition. The total weight of melts used in the experiment is counted as 0.5-15 tons. Here some interesting phenomena were found. If the mixture of raw materials were unevenly mixed in the casting stone would be presented some black nodes consisting of chromite (about 25%) and silicate glass (about 75%) and varying from 5mm to 5cm in size. In these black nodes the content of Cr2O3 is always about 30 times as much as that of the casting stone which encloses the former. The observations and experiments show that the black nodes were formed from the powder coal ash as a basal material. The FeO*/Cr2O3 ratio in these black nodes is approximately a constant 1.10 (Tab. 1). The distribution coefficients of Cr2O3 and MgO in these nodes and coexisting casting stone KDCr and KDMg are 33 and 0.69 respectively (Tab. 4). It shows that in the case of temporary coexistence of two liquid phases, i.e. the melts of black nodes and casting stone, under a non-equilibrium condition the content of a certain material presented in the both phases must be controlled by the distribution law. As two liquid phases of which one is rich in Al2O3 and FeO or Fe2O3 were co-existed in the system of Cr2O3 of basaltic magma, Cr2O3 would be extracted by this liquid phase.These experiments show that the assimilation of the argillaceous wall rocks by magnesian basic or ultrabasic magma is favorable to the enrichment of chromite.The author’s experiments also indicate that when the content of (FeO+Fe2O3) in raw materials was adjusted to approach that in power coal ash, the black nodes could not be formed even though the mixture of raw materials was unevenly mixed. In this case the chromite is dispersed in the casting stone completely. Therefore, the experimental results set up an explanation why ferriferous basic or ultrabasic magma is unfavourable to the formation of chromite deposits.