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Luzon, Philippines
Main commodities: Cu Au

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The Guinaoang porphyry copper-gold deposit is located in Benguet Province, Luzon in the Philippines, 95 km by road north of Baguio City and 6 km to the south-east of Lepanto in the Mankayan district.

The oldest rocks in the district are strongly folded submarine basaltic to andesitic volcanics and cherts, and turbiditic sedimentary rocks of possible Late Cretaceous to Palaeogene age. These are unconformably overlain by an Miocene andesitic volcanic pile, which grades laterally into volcaniclastic conglomerates and siltstones. These rocks are intruded by a north-south trending, dominantly tonalitic batholith dated at between 13±0.8 and 12±0.4 Ma. A series of poorly exposed stocks of quartz diorite porphyry were emplaced in the Mankayan district to the east of the main batholith, at least four of which are mineralised. These have been dated at 3.5±0.9 Ma. These are in turn overlain by a sequence of dacitic pyroclastics and subordinate lavas, occurring as as series of diatremes and endogenous domes of Pliocene age (2.9±0.4 Ma). The youngest sequence comprises a thin veneer of poorly consolidated dacitic air-fall tuff. The western margin of the district is defined by a complex north-south to NNW-trending fault zone, a splay of the maor Philippines Fault.

Copper and gold mineralisation at Guinaoang is associated with a blind, Pliocene, steep-sided quartz diorite porphyry stock that intrudes basement of Mesozoic biotite schsit and up to 1000 m of overlying andesitic volcanic rocks. Following the mineralisation, an upwardly flaring diatreme complex and subsequent dacite porphry dome destroyed part of the orebody. The diatreme is represented by an unbedded biotite-hornblende dacitic lapilli tuff, a grey lithic-lapilli tuff with ubiquitous clastic pyrite garins, and a coarse lithic breccia with a variety of clasts in a silty matrix. The twin peaks of the stock, separated by a saddle, are encountered along a steep sided ridge at a depths of 230 to 520 m along its 1000 m length. The stock expands with depth, such that at around 1000 m below surface it is 500 m wide, with walls that generally dip at from 70° to vertical. One of the dykes that emanate from the peak of the stock outcrops over a limited area. The porphyry consists of phenocrysts of plagioclase (oligoclase), rounded quartz-eyes, tabular hornblende and boiotite, set in a fine-grained hypidiomorphic-granular groundmass.

Alteration and mineralisation within and peripheral to the intrusion comprises: (1) early biotite- and magnetite-rich K silicates with minor chalcopyrite and bornite, and lesser pyrite; (2) variable sericite-clay-chlorite with a low suphide and high magnetite + hematite content, with chalcopyrite dominating over bornite; (3) Sericite dominated alteration, with a high associated pyrite content and absence of iron oxides, and bornite > chalcopyrite content; (4) Late-stage advanced argillic (quartz-alunite) alteration that produced an extensive (1.5 sq. km, and 200 to 300 m thick), planar cap to the alteration system, as well as occurring a widely spaced veins at deeper levels (as deep as 650 M). At both levels this alteration style carries enargite, luzonite, covellite and chalcocite, along wih other exotic copper minerals and abundant pyrite.

The reserves and resource released by Bezant Resources, 2010 were:
    Probable reserve - 189.6 Mt @ 0.46% Cu, 0.49 g/t Au,
    Indicated resource - 221.6 Mt @ 0.49% Cu, 0.52 g/t Au,
    Inferred resource - 36.2 Mt @ 0.44% Cu, 0.48 g/t Au,

    Total mineable inventory - 389 Mt @ 0.38% Cu, 0.42 g/t Au,

The most recent source geological information used to prepare this decription was dated: 1997.    
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd.   Unauthorised copying, reproduction, storage or dissemination prohibited.

  References & Additional Information
   Selected References:
Sillitoe R H, Angeles C A  1985 - Geological characteristics and evolution of a gold rich porphyry copper deposits at Guinaoang, Luzon, Philippines: in   Conference Proceedings - Asian Mining 85 IMM, London    pp 15-26

Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge.   It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published.   While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo, its employees and servants:   i). do not warrant, or make any representation regarding the use, or results of the use of the information contained herein as to its correctness, accuracy, currency, or otherwise; and   ii). expressly disclaim all liability or responsibility to any person using the information or conclusions contained herein.

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