Abstract

MUTTI, Diana; DIMARCO, Alejandro; MENDEZ, Carolina  and  KORZENIEWSKI, Lidia. Textures,fluid inclusions and stable isotopes in quartz-auriferous tensional veins ofPaleozoic shear zones, Eastern Sierras Pampeanas. Rev. Asoc. Geol. Argent. [online]. 2009, vol.64, n.3, pp.458-471. ISSN 0004-4822.

In Sierras Pampeanas, conspicuous FamatinianOrdovician - Silurian shear zones crop out, with brittle to brittle - ductiledeformations. In the Devonian - lower Carboniferous, these shears werereactivated by the superimposing achalian orogeny in a brittle - ductile tobrittle regimen, transitional to brittle in the last evolution stage. Tensionalveins synchronically developed in the shear systems, after the achalianDevonian magmatism, were filled with white1, white to transparent grey₂,grey₃ and chalcedonic₄ quartz, bearing gold, W - Fe - Bi oxidesand base metal sulphides. The deposition of gold in the quartz vein systems andthe precipitation of base metal sulphides (< 15 % per volume) was the mostimportant process in stage₃; these metals arranged in chains anddisseminations in the microcrystalline grey quartz. The stage₃quartz appears in veinlets and bands, related to strain sites in the whitemilky and transparent grey quartz's, and determines mainly laminated, ribbonand stockwork textures. We emphasise in the grey₃ quartz, throughmacro and microstructurals, termobarometric, fluid inclusions and δ¹⁸O isotopesstudies, with complementary information about massive white1 and chalcedonic₄quartz's, and metamorphic and igneous basement rocks. The results point out theexistence of double and triple phases in the fluid inclusions, withhomogenisation temperatures around ~ 278 °C, lower salinities (< 5,22NaCleq) and fluid pressures (Pint < Pconf), and hydrothermal fluid signaturederived from magmatic and/or metamorphic sources. Moreover, the stage₃is related with deformational process, neomineralization and tensional fracturefilling in rheologic brittle conditions, and interaction between hydrothermalfluid and basement rocks, during the achalian orogeny final phase. Furthermore,the results show that meteoric water participated in the final stage₄due to the Sierras Pampeanas uplift since the Devonian.

Keywords : Achalian shears; Grey quartz; Gold; Textures; Fluid inclusions; Stable isotopes.

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