Runruno, Malilibeg South
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The Runruno and Malilibeg South gold molybdenum deposits are located ~200 km north of Manila and ~70 km ENE of Baguio in the province of Nueva Viscaya, north-central Luzon, in the Philippines (#Location: 16° 24' 27"N, 121° 19' 22"E).
These deposits lie within the North Luzon Terrain, which is at the northern end of the Philippine Mobile Belt, juxtaposed against terrains to the west and south by splays of the Philippine Fault, a major structure that spans the full length of the Philippines archipelago.
Runruno and its southern extension, Malilibeg South are regarded to be alkaline type epithermal deposits. They are located ~20 km NW to NNW of the Didipio porphyry copper-gold deposit in a similar tectonic and regional geologic setting. For a more detailed description of the regional geology and setting of the units and intrusives described below, see the separate Didipio-Dinkidi record.
Runruno is hosted by the Palali Intrusive Complex, one of the three late Oligocene to early Miocene alkalic intrusive complexes developed just beyond the southern tip of the regional Cagayan Valley basin. Didipio is associated with another of these three intrusions, the Didipio Complex. The Palali batholith comprises light pinkish grey, typically equigranular, medium- to coarse-grained potassic syenites, nepheline syenite and nepheline monzosyenites which were intruded into the subalkaline volcanic succession of the Mamparang Formation ~15 km to the NW of Didipio (Albrecht and Knittel, 1990). K/Ar age dating of the Palali Batholith (MMAJ,1977) gave ages from 25 to 17 Ma, although the younger may be the result of argon loss due to thermal resetting (Albrecht and Knittel, 1990). If so, the Palali Batholith has an age comparable to the porphyry Cu-Au mineralisation at Diilkidi (Albrecht and Knittel, 1990; Knittel, 1983; Wolfe et aI., 1999).
The Palali Intrusive Complex comprises three main phases, a southern syenitie body, a northern nepheline syenite body, and a small central mass of nepheline monzosyenite, which have intruded what is interpreted to be a small caldera structure (Albrecht and Knittel. 1990). The nepheline syenites and monzosyenites predominantly composed of alkali feldspar and plagioclase, with 8 to 12% modal nepheline and accessory clinopyroxene, amphibole, magnetite, biotite, apatite and sphene. Alkaline trachyte lavas and pyroclastics of the Upper Mamparang Formation are associated with the intrusions, and are considered to be late stage caldera fill ignimbrites. Pseudoleucite-phyric trachyte dykes intrude the alkaline Late Oligocene Mamparang Formation (MMAJ, 1977) and Early Miocene Upper Mamparang Formations (Albrecht and Knittel. 1990).
The Runruno deposit is located on the western edge of a ~3.5 km diameter alkaline volcanic complex, the Runruno Volcanic Complex, at its intersection with a second district-scale calderas and major NE and NW trending fault lines, and in the vicinity of several late, small volume, composite volcanic centres. The immediate area is predominantly underlain by silica-under-saturated, alkali-rich intrusive monzonite to syenite porphyry of the Palali Intrusive Complex. Coeval with these intrusions are thick sequences of trachytic, volcanoclastic and tuffaceous volcanics, volcanic breccias and agglomerates which are intruded by the syentic-monzonite and form a characteristic domal feature within the central part of the deposit area.
This significant local doming, accompanied by intensive alteration and mineralisation demonstrate the presence of the gold system. The area has extensive argillic alteration caps with north to NE trending linear zones of intense sulphide-phyllic alteration around the western and southern rim of the centre, with individual zones of the order of 1000 x 200 m. A broad, east-west aligned, 2600 x 800 m zone of moderate phyllic alteration is located on the northern margin of the volcanic centre. The argillic cap is present from an elevation of ~750 masl to the local highest Cobocbocan Peak at 970 masl. Mineralisation appears to be constrained between 500 to 750 masl, limited and concealed by the argillic alteration cap.
The gold mineralisation is distinct but quite rare in that quartz veining is absent, alteration and veining is dominated by adularia and the gold occurs mostly as fine disseminations associated with pyrite and significant, molybdenite. The major host unit is a crystal tuff capped by a coarse volcaniclastic fragmental.
The mineralisation style and lithologies at the Malilibeg South gold-molybdenum deposit are similar to the main Runruno deposit immediately to the north. It has been defined over a strike length of 550 m, and comprises a series of stacked, shallow dipping mineralised lenses. These lenses appear to be best developed in both width and grade in the immediate hanging wall of the north-south striking, moderate west dipping Malilibeg Fault, and along the fault zone itself, similar to the Runruno deposit. The combined mineralised intersections ranges from 2 to about 20 m in thickness.
JORC compliant ore reserve and mineral resource estimates are as follows (Metals Exploration Plc website, visited June 2016):
Measured resource - 11.2 Mt @ 1.88 g/t Au, 604 ppm Mo;
Indicated resource - 7.0 Mt @ 1.64 g/t Au, 425 ppm Mo;
Inferred resource - 7.5 Mt @ 1.44 g/t Au, 253 ppm Mo;
TOTAL resource - 25.7 Mt @ 1.69 g/t Au, 453 ppm Mo, containing 43.2 t of Au.
Proved reserve - 10.2 Mt @ 1.90 g/t Au, 616 ppm Mo;
Probable reserve - 4.8 Mt @ 1.77 g/t Au, 415 ppm Mo;
TOTAL reserve - 15.0 Mt @ 1.85 g/t Au, 603 ppm Mo.
Inferred resource - 7.55 Mt @ 1.4 g/t Au, 1200 ppm Mo, containing 10.6 t of Au
This summary is based on details on the Metals Exploration Plc website (visited June, 2016) and from "Taylor, I., 2013 - Runruno Project, Malilibeg South Resource, Nueva Viscaya Province, Philippines; a report prepared by Mining Associates Pty Limited for FCF Minerals Corporation, 20p."
The most recent source geological information used to prepare this summary was dated: 2016.
This description is a summary from published sources, the chief of which are listed below.
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