Ahmed, et al., report that based on a global compilation of whole-rock geochemical data, Sr/Y and Sr/MnO are identified as effective discriminators between ore-forming and unprospective intrusions in the porphyry Cu setting. Intrusive rocks are classified into three fertility groups: prospective, unprospective, and mixed-signal, which are designed to assist explorers as a discrimination tool, narrowing the exploration search-space in porphyry Cu districts.
Portable X-Ray fluorescence (pXRF) data of Sr, Y and MnO were collected on pulp powders and rock slabs from six porphyry Cu (± Mo ± Au) districts. Pre- and post-mineralization intrusions from porphyry Cu districts have lower Sr/Y and Sr/MnO values than synmineralization intrusions from the same districts, although absolute values were variable between districts. PXRF data were compared to conventional whole-rock data to determine if pXRF data were appropriate substitutes for conventional whole-rock methods of evaluating the ore-forming potential of intrusive rocks. PXRF data collected on pulp material were found to be more accurate (<16% of conventional methods) and more precise (<5% relative standard deviation) than those collected on intact rock slabs (<37% of conventional methods; <24% relative standard deviation). These differences are attributed to the grain size and mineral homogeneity of samples. Despite the low precision of pXRF analyses on individual rock
slabs (mean RSD of 24% Sr/Y and 32% Sr/MnO), mean values for each sample plot in the expected fertility field on the Sr/Y and Sr/MnO diagram. Our results demonstrate that in situ pXRF data collection provides an effective discriminator of Cu fertility, and represents a powerful field exploration tool.
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