The multi-attribute anomaly structure model: An exploration tool for the Zhaojikou epithermal Pb-Zn deposit, China

Abstract

Traditionally, a geochemical exploration index is based mainly on elemental concentration, and focusses on positive anomalies rather than negative anomalies. This results in two problems: firstly, it ignores depleted elements, negative anomalies, and immobile elements, and secondly, elemental concentration does not directly reveal the degree of elemental mobility. To discover information on element mobility and utilize negative anomalies, the Isocon method was employed to calculate mass-transfer, and study anomalous elemental characteristics in the Zhaojikou epithermal Pb-Zn deposit, SE China. Subsequently, the concept of a multi-attribute anomaly structure is proposed, which refers to enrichment and depletion zones of multiple elements co-existing in an ore deposit. This includes major elements, mineralizing agents, and ore-forming and associated elements.Results show that there are system mass-transfer (μ), Na2O, and S anomalies, correlations between S-FeO-Pb+Zn, and Pb, Zn, Cu, Ag, As, and Sb anomalies in the multi-attribute anomaly structure model of the Zhaojikou Pb-Zn ore deposit. The presence of the μ anomaly indicates there was at least one mass-exchange geological event, with the extent of the anomaly representing the impact area of the event(s). The extent of the negative Na2O anomaly represents the fluid-rock interaction zones. The positive S anomaly suggests the presence of sulphides. The correlations between S-FeO-Pb+Zn reveal there are numerous other economic metal sulphides (i.e., excluding noneconomic Fe-rich sulphides like pyrite). Ore-forming and associated elemental anomalies indicate the potential presence of polymetallic sulphides. μ>0.3, ΔCNa2OO-A<−7kg, and μNa2O<−50% can act as evaluation indices for ore prospecting. There are two anomalous centres in the Zhaojikou Pb-Zn ore deposit. The shallower and larger one corresponds solely to the presence of the known orebodies. However, the deeper and smaller one is not currently known, and suggests ores may be present at depth. In summary, the Zhaojikou district has great potential for additional ore deposits at depth. We suggest directing further work deeper, mainly along NE–SW Dongzhi Fault.