Geochemistry of gold quartz vein walls from Jales (northern Portugal)

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Authors:Neiva, A. M. R.; Neiva, J. M. C.; Silva, M. M. V. G.
Author Affiliations:Primary:
Univ. Coimbra, Dep. Mineral. and Geol., Coimbra, Portugal
Volume Title:Chemical Geology
Source:Chemical Geology, 82(3-4), p.217-251. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0009-2541
Publication Date:1990
Note:In English. 29 refs.; illus. incl. 12 tables, geol. sketch maps
Summary:The long hydrothermal quartz veins from Campo de Jales have been exploited for Au and form the main Portugese Au deposit. Au and electrum occur in sulphides, sulphosalts and quartz and in thin veinlets along fractures with sulphides, while Ag occurs in electrum, argentite, galena and most of the sulphosalts. The Campo Au quartz vein cuts mainly the Hercynian peraluminous medium- to coarse-grained porphyritic seriate two-mica granite and also the pre-Ordovician biotite-muscovite-andalusite schist with sillimanite. At 1-0.5 m from the vein the granite is altered into a porphyritic muscovite-biotite granite, while adjacent to the vein, < or equal to 0.5 m, it is a muscovite granite. At 3 m from the vein the mica schist shows some metasomatic effects, but it is transformed into a biotite-muscovite-brunsvigite at 2 m from the vein and into a mica schist enriched in muscovite and sulphides adjacent to the vein in a zone of 0.1-0.5 m up to 1 m from the vein. There are progressive increases in SiO2, Fe2O3, K2O, H2O+, S, As, Sn, Sb, Cu, Pb, Rb, Au, a negative Eu anomaly and progressive decreases in TiO2, FeO, MgO, CaO, Cl, Li, Sr, Th and all REE with increasing degree of hydrothermal alteration of granite. K2O, F, S, Rb and Cs progressively increase, while FeO, CaO, Zr and Sr decrease with increasing hydrothermal alteration of mica schist. At the direct contact with the vein the granite and mica schist show enrichment in K2O, Fe2O3, H2O+, Sn, Rb, S, As, Zn, Sb, Cu, Pb and Au, and impoverishment in TiO2 MgO, FeO, CaO, Na2O, Cl, Cr, V, Nb, Li Ni and Zr, which gives information on the ore-forming fluids. The hydrothermal alteration of granite increases with depth, but seems to decrease with increasing distance from the granite-schist contact. The unaltered granite was emplaced at approx 3 kbar and 690 degrees C and of 10-18bar, but was completely crystallized at 460-600 degrees C. It was hydrothermally altered at 200-400 degrees C and <1-2 kbar. [P.Br.]
Subjects:Economic geology; Geochemical controls; Geochemical methods; Geochemistry; Gold ores; Hydrothermal alteration; Metal ores; Metasomatism; Mineral deposits, genesis; Mineral exploration; Ore guides; Ore-forming fluids; Processes; Quartz veins; Trace elements; Veins; Wall-rock alteration; Europe; Iberian Peninsula; Portugal; Southern Europe; Campo de Jales; Hydrothermal processes; Jales; Northern Portugal
Abstract Numbers:90M/4321
Record ID:1990048309
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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