Metallogenic efficiency from deposit to region–A case study in western Zhejiang Province, southeastern China

Abstract

Metallogenic (ore) efficiency can be defined as the ratio of metal reserves to its total supply, and we expanded a typical efficiency-calculation model available at the single mineral scale to the regional scale. A new cell-based model was developed by analogy and by taking some other influences into account: i) a thicker sedimentary cover; ii) regional ore- and rock-controlling structures and their intersections; iii) the crustal heterogeneity unrelated and related to ores; and iv) metallic geochemical anomalies. Finally, a regional contour map of weighted efficiency, which is essential to metallogenic prediction, was obtained. It shows that the efficiency anomalies can provide a much better target area for ore-positioning than do metallic content anomalies, and greater ore efficiency may indicate the likelihood of occurrence of mineral deposits that are larger in size (reserves). Taking northwestern Zhejiang province as a case study, in which the geochemistry of Mesozoic porphyries plausibly show considerable mineralized potential, we found that due to the lower magmatic temperature, delayed exsolution of the hydrothermal solution, and very thick sedimentary cover, the Cu-polymetal ore efficiency associated with granitic plutons in this area is generally low; the relatively higher ore-productivity (efficiency) appears mainly in and around small rock bodies, rock margins, and the contacting zone between different lithologies. Most ore spots, no matter their size, fall into areas with nonzero efficiency values. There seems to be no interdependence between most ore spots of smaller size and ore efficiency, whereas efficiency is essential to regional small- and medium-scaled metallogensis.