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| Index > Projects > Tampakan > The Deposit |
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 The Tampakan copper-gold deposit represents a major high-sulphidation epithermal deposit superimposed on an underlying porphyry copper system. The deposit is hosted by a sequence of andesite flows and associated diorite intrusives related to a highly eroded andesitic stratavolcanic complex of Pliocene age ( Figure 3 ). This stratovolcanic complex is interpreted to lie on the northern extension of the Sangihe volcanic arc that extends from Northern Sulawesi in Indonesia . The Tampakan district is located within a complex tectonic setting dominated by WNW trending wrench faults that form part of the trans-Mindanao Cotabato Fault Zone. The Tampakan deposit is located near the intersection of one of several WNW trending splay structures with a prominent NNE trending dilational structure, one of many that transect the host volcanic complex.
High-sulphidation style copper-gold mineralisation at Tampakan is broadly associated with and central to a flat-lying tabular body of pervasive silica and silica-clay alteration developed within a district-scale cap of advanced-argillic and argillic hydrothermal alteration that extends over an area of 90 square kilometers within the volcanic complex.
At an approximate 0.3% copper contour, the Tampakan deposit comprises a flat-lying to gently dipping, tabular body of mineralisation extending over an area of 2km by 7km and ranging in thickness from 200-400m. Deposit geology has been developed from a systematic program of diamond drilling that currently comprises 157 completed holes (59,220m) with most holes ending in lower grade (0.2-0.4%Cu) porphyry-copper style mineralisation at downhole depths of 350-500m. Drilling density generally varies from 80m x 80m over selected higher-grade parts of the deposit to 160m x 160m elsewhere ( Figure 4 ). Some sections of the deposit remain with a low density of drilling varying from 160m x 320m to 320m x 320m.
( Table 1 ) lists selected high grade downhole intersections from the deposit that satisfy the selection criteria of = 100 metre% copper and = 1% copper. Selected drillhole assay sections through the deposit from north to south are attached as follows:
Superimposed high-sulphidation mineralisation and associated alteration passes transitionally to porphyry copper style mineralisation and alteration at depth. The interface between these styles of mineralisation can be quite irregular as a result of structural control on hydrothermal fluids.
High-sulphidation epithermal mineralisation and alteration is strongly influenced by the interplay of stratigraphic and structural controls, in particular NNE-trending dilatant faults. This style of mineralisation is typically associated with silica and silica-clay alteration assemblages that have obliterated or overprinted original textures and mineralogy. Sulphide mineralisation typically comprises the copper-rich species digenite, bornite, and enargite, and to a lesser extent chalcocite and covellite, and usually occurs as fractures, veins and vug-fills or as disseminations at depth. Pyrite is usually present throughout and enargite (an arsenical copper sulphide) distribution appears to be preferentially associated with late-stage structures and areas of strong silicification.
Porphyry-copper style mineralisation at depth comprises disseminated chalcopyrite, bornite and pyrite associated with variably developed quartz-stockwork veining. This mineralisation style is usually associated with clay alteration of host andesite and high-level hornblende diorite stocks and may represent the intermediate shell of a porphyry system. The metal grade in structural zones within the porphyry system is locally upgraded by high-sulphidation overprinting events, resulting in a change of sulphide mineralogy and progressive alteration of the host sequence.
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