Super enrichment of critical elements:Implications for stratgic mineral resources
The strategic mineral resources contain 56 critical elements,most of which have low crustal abundance and require 10-1000 folds of enrichment to form ore deposits.This results in extremely uneven distribution of mineral resources.Thus the delineation of super enrichment area is the key to the resource prospecting and discovery of large-sized ore deposits.The enrichment intensity of elements can be quantitatively expressed by the metallogenic acumulatioin index(m.a.i),the tonnagea acumulatioin index(t.a.i)and the anomalous concentration index(a.c.i).Statistical analyses of 35 strategic mineral species,including precious,non-ferrous,ferrous,rare and dispersed elements,rare earth elements and radioactive metals,revealed that(1)elements with a m.a.i greater than 1000 were antimony,bismuth,rhenium and gold;a m.a.i of＞100-1000 were silver,tungsten,tin,chromium,lithium,cesium,tellurium,indium,uranium and platinum group elements;and a m.a.i of＞10-100 were copper,nickel,chromium,beryllium,rubidium,scandium,niobium,tantalum,zirconium and primary rare earth elements.Iron,aluminium,titanium and ion-adsorbed rare earth elements had a m.a.i ≤10.(2)Large-sized ore deposits should have a t.a.i greater than 107,generally 1010,and a a.c.i greater than 2.0.Indicators for element super enrichment also included anomaly greater than＞100-1000 km2,with anomalous hierarchical structure across more than three layers,and with occurence of at least four associated elements.The element enrichment factor and potential resources in a geochemical block may be estimated using areal and cubic metal contents.The qualitative and quantitative geochemical characteritics of element super enrichment provide evaluation criteria for the assessment and discovery of large-sized mineral deposits.
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