Abstract
Abstract. In this work we have performed a detailed study of vectors to ore to a representative volcanic-rock-hosted replacive volcanogenic massive sulfide (VMS) deposit located in the northern Iberian Pyrite Belt (Spain), the Aguas Teñidas deposit. The investigated vectors include the following: (1) mineralogical zoning, (2) host sequence characterization and mineralized unit identification based on whole rock geochemistry discrimination diagrams, (3) study of the characteristics and behaviour of whole rock geochemical anomalies around the ore (e.g. alteration-related compositional changes, characteristics and extent of geochemical halos of indicative elements such as Cu, Zn, Pb, Sb, Tl, and Ba around the deposit), and (4) application of portable X-ray fluorescence (p-XRF) analysis to the detection of the previous vectors. In the footwall, a concentric cone-shaped hydrothermal alteration zone bearing the stockwork passes laterally, from core to edge, from quartz (only local) to chlorite–quartz, sericite–chlorite–quartz, and sericite–quartz alteration zones. The hydrothermal alteration is also found in the hanging wall despite being tectonically allochthonous to the orebody: a proximal sericite alteration zone is followed by a more distal albite-rich one. Whole rock major elements show an increase in alteration indexes (e.g. AI, CCPI) towards the mineralization, a general SiO2 enrichment, and FeO enrichment as well as K2O and Na2O depletion towards the centre of the hydrothermal system, with MgO showing a less systematic behaviour. K2O and Na2O leached from the centre of the system are transported and deposited in more external areas. Copper, Pb, and Zn produce proximal anomalies around mineralized areas, with the more mobile Sb, Tl, and Ba generating wider halos. Whereas Sb and Tl halos form around all mineralized areas, Ba anomalies are restricted to areas around the massive sulfide body. Our results show that proposed vectors, or adaptations designed to overcome p-XRF limitations, can be confidently used by analysing unprepared hand specimens, including the external rough curved surface of drill cores. The data presented in this work are not only applicable to VMS exploration in the Iberian Pyrite Belt, but on a broader scale they will also contribute to improving our general understanding of vectors to ore in replacive-type VMS deposits.
Highlights
Volcanogenic massive sulfide (VMS) deposits represent a major source of base (Cu, Pb, Zn), precious (Ag, Au), and other metals (e.g. Co, Sn, In, Cd, Tl, Ga, Se, Sb, Bi) of economic importance (Large et al, 2001a; Franklin et al, 2005)
Trace elements were analysed by inductively coupled plasma atomic emission spectroscopy (ICP-AES) and inductively coupled plasma mass spectrometry (ICP-MS) on samples prepared by Na2O2 / NaOH fusion followed by dissolution in nitric acid; fusion was performed at low temperatures, which reduces the loss of volatile elements
At Aguas Teñidas it was first studied from the observation of the eastern sector of the deposit by Bobrowicz (1995), Hidalgo et al (2000), McKee et al (2001), and McKee (2003); they focused on the footwall and described a quartz alteration zone at the core of the hydrothermal system which passes laterally to chlorite, sericite–chlorite, and sericite alteration zones (Fig. 4)
Summary
Volcanogenic massive sulfide (VMS) deposits represent a major source of base (Cu, Pb, Zn), precious (Ag, Au), and other metals (e.g. Co, Sn, In, Cd, Tl, Ga, Se, Sb, Bi) of economic importance (Large et al, 2001a; Franklin et al, 2005). G. Gisbert et al.: Vectors to ore in replacive VMS deposits of the northern Iberian Pyrite Belt for improved efficiency and lower impact in both environmental and social terms. Gisbert et al.: Vectors to ore in replacive VMS deposits of the northern Iberian Pyrite Belt for improved efficiency and lower impact in both environmental and social terms In this context, the combined study of VMS mineral systems and the development of new exploration strategies and technologies based on geophysical methods and vectors to ore play a vital role
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