PB-ISOTOPE AND TRACE ELEMENTS ANALYSIS BY LA-Q-ICPMS OF GALENA FROM ARGENTINIAN EPITHERMAL DEPOSITS: A PRELIMINARY ANALYSIS

MAYDAGÁN, LAURA; MCFARLANE,CHRISTOPHER; LENTZ, DAVID; BOUHIER, VERÓNICA; CAFFE, PABLO; RAINOLDI, ANA LAURA; PONS, JOSEFINA; FERNÁNDEZ, MARÍA LIS; FRANCHINI, MARTA; LUNA, GERALDINE

Salta

Congreso; 15th Quadrennial International Association on the Genesis of Ore Deposits Symposium; 2018

BACKGROUNDIn situ laser ablation quadrupole inductively coupled plasma-mass spectrometry (LA-Q- ICPMS) allows us toobtain rapid, accurate, and precise Pb isotope measurements together with trace elements in galena (McFarlane etal., 2016). Recent investigations have shown that galena can host a broader range of elements than previouslyrecognized, many of them (e.g., Ag, Bi, Se, Te) can be extracted as by-products of an ore containing galena andothers (Sb, Cd, Tl) existas impurities (George et al., 2015).Pb isotopic studies have been applied as a tool in exploration of metallogenic terrains based on comparing theisotopic compositions of existing deposits within a district to prospective showings. Bouhier et al. (2017) presentedPb isotopic data of the Navidad Ag world class epithermal deposit. These authors indicated that the Pb isotopic ratiosof Jurassic volcanic rocks and ore minerals from epithermal deposits of Patagonia have distinctive signatures in theNorth Patagonian Massif, the Deseado Massif, and the Andean region that vary with time in the volcanic events ofthe Chon Aike Volcanic Province.The objective of this contribution is to present new Pb isotopic data and trace elements obtained with themethod LA-Q-ICPMS in galena from epithermal deposits in Argentina in order to identify patterns at regional andlocal scales that may be useful in exploration or exploitation.METHODSSamples of galena were selected from epithermal deposits of Argentina: Navidad mining district (LomaGalena, Loma La Plata and Valle Esperanza deposits, hosted by Jurassic volcanic rocks, Chubut Province, NorthPatagonian Massif) Virginia and La Paloma (hosted by Jurassic volcanic rocks, Santa Cruz Province, El DeseadoMassif), Chinchillas (hosted by Miocene volcanic rocks, Jujuy Province, Northern Puna), and Andacollo deposit (hostedby Carboniferous and Permian volcanic rocks, Neuquén Province). Polished thin sections of galena were analyzed bythe quadrupole LA-ICP-MS facility at the Department of Earth Sciences of the University of New Brunswick,Fredericton, Canada (McFarlane et al., 2016).RESULTSGalena from Chinchillas and Andacollo yields the highest 207Pb/204Pb ratios (average values 15.631 and 15.642Chinchillas; 15.651 Andacollo), whereas the less radiogenic 207Pb/204Pb ratios are recognized in galena from Patagonia:Virginia (15.587) and Loma La Plata (15.571-15.627).The 206Pb/204Pb results are highest in galena crystals from Chinchillas (18.583-18.618) and Andacollo (18.497)and lowest in galena from the Navidad mining district (18.231-18.262), whereas galena from La Paloma and Virginiayield intermediate 206Pb/204Pb ratios.Galena crystals from Andacollo and Chinchillas deposits show higher 206Pb/204Pb and 208Pb/204Pb ratios thansamples of galena from Patagonia (North Patagonian and Deseado Massifs). Samples of galena of epithermaldeposits from the Deseado Massif (La Paloma and Virginia) yield higher 206Pb/204Pb ratios than samples from theNorth Patagonian Massif (Navidad mining district).The 208Pb/204Pb ratio is highest in galena from the Chinchillas deposit (average values of 38.750 and 38.827)and lowest in the samples from the Navidad mining district (average values of 38.203 and 38.311).Silver is the most abundant trace element in the crystals analyzed. The highest mean concentrations of Ag wererecorded in samples from epithermal Ag-rich deposits from Patagonia (e.g., Navidad 9958 ppm, Virginia 5901 ppm). InLa Paloma deposit, galena has average contents of 127 ppm Ag. Samples from Andacollo deposit have mean values ofAg of 895 ppm, and two samples of galena from Chinchillas have average values of 3510 and 4471 ppm Ag.Mean Sb concentrations in galena crystals show a wide range, from 2.7 ppm in a sample from Navidad depositto 4412 ppm in galena from Chinchillas deposit. The highest concentrations of Bi were obtained in galena from theAndacollo deposit (mean value of 92 ppm).Selenium concentrations vary over 3 orders of magnitude in the studied samples. Galena from La Palomashows the highest Se contents. The highest mean Cd concentrations were obtained in galena crystals from Navidad (262 ppm) and La Paloma (190 pmm) deposits. In Virginia, Andacollo, and Chinchillas, Cd values are very low, withmean concentrations ranging from 17 to 23 ppm. Tellurium concentrations in galena from the Andacollo depositshow a wide range of values (26 to 1060 ppm) with a mean of 150 ppm Te.CONCLUSIONSWe present new Pb isotopic data and trace elements in galena from Argentinian epithermal deposits. The Pbisotopic data obtained allow correlate galena to geological provinces and ages. Within the Patagonia it is possible todifferentiate galena from the Deseado Massif and the North Patagonian Massif according to their isotopic signatures,especially their 206Pb/204Pb and 208Pb/204Pb ratios. We suggest that these analyses could be useful to identifymetallogenetic events in Patagonia and could be applied in regional mining exploration complemented withconventional exploration techniques.Pb isotopes in galena from Chinchillas have the same signatures as the Eastern Cordillera basement domaindefined by Aitcheson et al. (1995) and the Antofalla domain of Mamani et al. (2010). The similarity in isotope ratioswith host volcanic rocks and regional volcanism (e.g., Caffe et al. 2002) suggests that Pb isotope compositions ofChinchillas ores were inherited from magmas in which the basement participates through different mechanisms(mixing of crustal and arc melts or as contaminants in AFC processes) that affect Puna backarc magma evolution(Caffe et al., 2002; Kay et al., 2010).Regarding trace elements, large standard deviations recognized in Ag and Sb contents in Navidad, Virginiaand La Paloma samples, are interpreted as the result of nano-inclusions of Ag mineral phases and Sb-sulfosalts ingalena. The relative low standard deviations recognized in Andacollo and Chinchillas samples suggest that Ag and Sbin these crystals could be present as solid solution.Similarly, low standard deviations in Se from La Paloma galena crystals suggests its presence in solid solution.Bismuth values show high standard deviations in all the samples consistent with the presence of sub-micron-size Bibearingphases. The wide range of values of Te in Andacollo deposit suggests microinclusions of telluride minerals.