The MAMA ratio: An index that quantifies genetic and geometallurgic relationships

A comprehensive quantitative mineralogical study on the Hämmerlein tin deposit in the Erzgebirge, Germany, yields not only insights into the genesis of Sn mineralization but provides also important clues for beneficiation. The lithological units of the skarn and greisen deposit show significant differences in modal mineralogy and Sn deportment. These systematic differences are attributed to several stages of ore formation. Of greatest significance is a paragenetically late cassiterite-chlorite-fluorite-sulfide assemblage. This assemblage replaces pre-existing skarn lithologies and also forms stockwork mineralization in greisen-type ores developed at the expense of mica schist that surrounds the skarn. The co-genetic formation of the cassiterite-chlorite-fluorite-sulfide assemblage is captured by the mineral association parameter – a parameter that can be easily quantified from data acquired during automated mineralogy studies. To document the preferred mineral association a ratio is introduced that illustrates how closely cassiterite – the only Sn mineral of economic relevance – is associated with chlorite, fluorite and sulfides. This so-called MAMA ratio illustrates the strongly preferred association between cassiterite and chlorite. The same data can also be used to deduce constraints and opportunities for beneficiation. The case study illustrates the inherent link between ore genesis and process mineralogy – a link that should be considered in any geometallurgical assessment.