A Study On The Characteristics Of Leucocratic Alteration Zone Of Nihe Iron Deposit, Lujiang, Anhui

The Ni-He iron deposit is a large discovery recently found within the northwest ofLuzong volcanic basin of Middle and Lower Yangtze River metallogenic belt.With thesummary of the regional geology background,this paper focuses on the depositgeology,characteristic of leucocratic alteration zone and morphology of pyrite study toachieve some comprehensive acknowledgements on the aspects of geology andgeochemistry and genesis process of the deposit.The wall rocks is of an intense and pervasive alteration that shows a series oftypes,with multiple phases of time and a layered performance of lateral and a zoning ofvertical.According to alteration minerals assemblage, the alteration zones can bedivided into three types:a.The lower melanocratic alteration zone;b.The upperleucocratic alteration zone;c.The middle hybid alteration zone.Futhermore,the upperleucocratic alteration zone can be subdivided into three subzones in accordance withmineral assemblage and mineral spatial distribution:1.Water mica-kaolinite alterationsubzone;2.Secondary quartzite alteration subzone;3.Anhydrite alteration subzone.Variation of elements in the alteration zones shows some features that activities oftrace elements and rare earth elements become enhanced and variation range gets widerfrom the lower melanocratic alteration zone to the upper leucocratic alteration zone.Trace elements fractionate more obviously especially within the leucocratic alterationzone and the element of potassium is rich for the potassium-rich minerals widelyincluded in the Watermica-Kaolinite alteration subzone,the content of trace elements isthe lowest in the secondary quartzite alteration zone,LREE and U strongly enrich andEu is of positive anomaly in the anhydrite alteration subzone.Element migration shows some regularities subject to element geochemistry law andgeochemical environment during alteration process, especially within the leucocraticalteration zone.1.Anhydrite alteration subzone: Ca,S,Fe,Cu,Ag immigrate andSi,Ti,Mg,K and Na emigrate;2.Secondary quartzite subzone: a large number of silicateenriches and rare earth elements fractionate to show a HREE enrichment left-leaningmode.3.Kaolinite alteration subzone:S,Cu,Ag,Pb,MgO,Cao,K2O and P2O5immigrateand P2O5emigrates and rare earth elements show a feature of inertica,only slightly out.The pyrite typomorphic study shows that pyrites have a slight surplus of Fe, a slightloss of S, a large amount of Co,a low amount of Ni,a higher amount of Zn and a littlecontent of Pb not even reaching the detection limit. In addition, Se and Te show a high content and are easy to place S. Copper and Zinc and some other elements exist in theform of machinery foreign substance within pyrites.All the above show that the pyritedeposit is of a hydrothermal origin.Throughout characteristics of the magmatic ore deposit,wall rock alteration,diagenetic and metallogenic epoch, and other comprehensive analysis, the author arguesthat the Ni-He deposit relates to volcanic magmatic hydrothermal evolution and can beclassified into the type of porphyry iron deposit.