GEOCHEMICAL RELATIONS OF IN (INDIUM) BEARING SPHALERITE IN THE SAN ROQUE PROJECT (RÍO NEGRO PROVINCE, ARGENTINA).

LUNA L.; GRECCO L.E.; BONUCCELLI, R; GONZALEZ M.V.; GARRIDO M.M

Puerto Madryn

Congreso; XXI Congreso Geológico Argentino; 2020

AGA

Indium (In) is a metal used in high technologyespecially in semiconductors and liquid crystal displays (Nauckhoff von, 2011).They have been reported until now few indium discoveries in Argentina: ThePenguins project in the Deseado Massif (explored jointly by the INREMI andArgentex Company), El Peladar in Jujuy province (Zappettini et al., 2004) andSan Roque (SR) project in the North Patagonian Massif, explored by MarifilMines Limited Company. The San Roque property is located within Valcheta andSan Antonio Oeste departments, Río Negro province, covering an area of 11.381,5hectares.  Mineralization occurs as zonesof narrow, sheeted quartz-carbonate-sulphide veins and stockworks as well assulphide disseminations within host Jurassic volcanic and volcaniclastic rocks.The drill core chemical analysis indicate a direct relationship between the Incontent and abundant sphalerite and chalcopyrite. The aim of this work to studyin San Roque the geochemical characteristics of the In bearing sphalerite bymicroprobe analyses. The San Roque project is located in the northeastern NorthPatagonian Massif. In the area the following units are identified, the oldestrocks correspond to Valcheta Group and consist of low-grade metamorphic rocksof the Proterozoic Nahuel Niyeu Formation; theserocks have been intruded by granites of the Permian Paileman Formation. The In-bearing sphalerite mineralization is associated to the rocks of theMarifil Volcanix Complex (Cortés, 1981); these consist of felsic volcanic,volcaniclastic and subvolcanic porphyritic intrusions that overlie and cut thebasement metasedimentary strata. Rock samples from drilling cores were providedby the Company Marifil SA. Chalcographics sections were performed at PetrotomyLaboratorie of Geological Department, Bahia Blanca University. The In element was analyzed by ICP-MS ultratracefollowing Aqua Regia digestion. Electronmicroprobe analysis (EMPA) ofsphalerites were performed in the Lanmark (Córdoba University) on a Jeol JXA8230. The operating conditions were 15 KV and 10 nA.   The DDH4 dril l core is located in the ?Estructura delIndio? which was subdivided into three different mineral assemblages: (i)stockwork mineral association;(ii) quartz vein mineral association; and (iii)salar mineral association (arranged in order of decreasing age oremineralization) by Dill et al (2013). Samples of the DDH4 drill core were takenat different depths to observe variations in the composition of the sphaleritewith depth and correspond to the assemblage ( i) of Dill et al (2013).Sphalerite was analyzed from samples 7495a (Figure 1A), 7512 and 7530 taken atdepths of 77, 96 and 117 m respectively. Sphalerite can incorporate a diversesuite of chemical elements in its structure. A total of 48 electron microprobeanalyses were carried on sphalerite in the present study. Concentrations of eighteenelements (As, Ag, S, Au, Fe, Cu, Pb, Hg, Mn, Se, Sb, Te, In, Ni, Zn, Sc, Cd andCo) were determined at each point. The Fe, Cd and Cu commonly substitute for Znin sphalerite, whereas Pb, In, Ga, Ge, Hg, Sn occur more sporadically. The data results indicate that the chemicalcomposition of the sphalerite crystal is not homogeneous. The Zn content in sample7495a ranges from 64,877 to 67,194 wt% and averages 66,15 wt%; in sample 7512from 61,363 to 66,567 wt% and averages 64,197 wt%; and in sample 7530 from59,757 to 66,75 wt% and averages 64,627 wt%. The In content varies between0,005 and  1,108 wt% and averages 0,2031wt%; between 0,19 and 3,938 wt% and averages 1,5881 wt%; and  between 0,014 and 4,834 wt% and averages1,2306 wt% respectively. The Fe content in sample 7495a ranges from 0,301 to1,401 wt% and averages 0,8598 wt%, in sample 7512 from 0,268 to 1,062 wt% andaverages 0,5154 wt%, and in sample 7530 from 0,233 to 1,169 wt% and averages0,4982 wt%. The Cu content varies between 0,005 and 0,575 wt% and averages 0,1022wt%; between 0,018 and 2,046 wt% and averages 0,9148 wt%; and  between 0,011 and 2,904 wt% and averages0,7508 wt% respectively The diagram show a positive correlation between In withCu and Fe suggesting that substitution in sphalerite is dominated by the Cu?Fe metalpair, corroborating coupled (Cu+In3+) ↔ 2Zn2+ substitution (Figure 1B). A negative correlationbetween In and Ag, Au and Se is observed, and there is no correlation withother elements. In single crystals of sphalerite, indium reveals oscillatoryzoning with high and low-In concentration zones. This is interpreted as aresult of several pulses of the fluid with different concentrations ofelements.