The Occurrence Characteristics of Nickel and Molybdenum in Sedimentary Exhalative Polymetallic Deposit

Exhalative sedimentary polymetallic deposit is an attractive subject in the study of mineral deposit geology. Ascertaining the occurrence state of main ore components (nickel, molybdenum) is the important study focus for this kind of mineral deposit. The Swan Hill-Huangjiawan and Daping-Dahu nickel molybdenum ore belts of Xiang-Qian area are typical submarine exhalative sedimentary deposits. In this article, an account of samples that were collected from the ore district, and analyzed using large modern instruments including those for chemical and spectral analysis, Optical Microscope and X-ray Diffraction, Scanning Electron Microscope and Electron Probe is given, to study the occurrence states of nickel and molybdenum in the ores. The content of nickel was 3.76%, and the content of molybdenum was 4.99% using chemical and spectral analysis. Observations were made of the metal minerals in the polished section, which were distributed sporadically and occurred as fine particles. Since there is weak crystalline degree, low reflectivity and unclear crystal morphology under the polarizing microscope, it was preliminary inferred that the ore mineral existed in colloidal form, but it is difficult to name and describe these ore minerals. The X-ray Diffraction analysis results for the samples supported the observation under the Polarizing Microscope, which confirmed that there were many amorphous minerals hosted in the analyzed samples. The nickel and molybdenum occurred mainly in the tungsten-powellite and pyrrhotite with low contents of 0.4% and 0.8%, respectively. Comparing with the results of chemical analysis, it is hinted that there are other minerals which enrich nickel and molybdenum. Further analysis by electron microprobe in the nickel molybdenum enriched area indicate that nickel not only occurs in gersdorffite and vaesite, but is also concentrated in the edge of colloidal pyrite and pyrrhotite within a worm-like lace. Molybdenum mainly occurred in the carbon sulphur molybdenum ore. The nickel and molybdenum mainly occurred in the transition ore minerals from colloidal to crystalline. The research results provided important information and the basis for the study of ore mineralogy, mineral processing, smelting and comprehensive utilization of the mineral ores for this kind of deposit.