Gold-quartz veins at Gralheira, northern Portugal; mineralogical and geochemical characteristics

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Authors:Neiva, A. M. R.
Author Affiliations:Primary:
Universidade de Coimbra, Departamento de Ciencias da Terra, Coimbra, Portugal
Volume Title:Transactions - Institution of Mining and Metallurgy. Section B: Applied Earth Science
Source:Transactions - Institution of Mining and Metallurgy. Section B: Applied Earth Science, Vol.103(December), p.B188-B196. Publisher: Institution of Mining and Metallurgy, London, United Kingdom. ISSN: 0371-7453
Publication Date:1994
Note:In English. 11 refs.; illus., incl. 4 tables, geol. sketch map
Summary:The WNW-ESE trending hydrothermal Au-quartz veins in this area cut alternating mica schists and quartzites of mainly Ordovician age and, to the W, also cut a Hercynian muscovite-biotite granite. They have been prospected and developed to a depth of 300 m; reserves of 20 t Au have been estimated. The paragenetic sequence and chemical compositions of the ore minerals at Gralheira are generally similar to those of the Au-quartz veins at Jales to the S. Au, electrum and aurian Ag form inclusions in arsenopyrite, pyrite, galena, sphalerite, pyrrhotite and quartz and also occur in veinlets cutting these minerals. Ag was found in Au, electrum, aurian Ag, tetrahedrite, freibergite and owyheeite. The crystallization T of an early generation of arsenopyrite was estimated as 480°C and of the more common, later arsenopyrite as 430-300°C. Au, electrum and aurian Ag are generally included in the latter. Sphalerite crystallized at 307-100°C and monoclinic pyrrhotite may have been formed by the inverrsion of hexagonal pyrrhotite at 248°C. [R.E.S.]
Subjects:Chemical composition; Fractional crystallization; Geologic thermometry; Gold ores; Hydrothermal alteration; Magmas; Metal ores; Metasomatism; Mineral assemblages; Mineral deposits, genesis; Mineral exploration; Mineralization; Ordovician; Ore-forming fluids; Orogeny; Paleozoic; Polymetallic ores; Quartz veins; Temperature; Variscan Orogeny; Veins; Europe; Iberian Peninsula; Portugal; Southern Europe; Gralheira Portugal; Hydrothermal processes; Northern Portugal
Abstract Numbers:95M/2770
Record ID:1995021244
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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