EL1822 Fergusson, Goodenough and Sanaroa
Fergusson, Goodenough and Sanaroa are part of the D’Entrecasteaux Islands in Milne Bay Province, and are situated east of the southeast tip of mainland PNG. The islands are mountainous, rising to heights in excess of 2,000 metres and consist of steep dome shaped ranges.
The gold potential of these islands was not significantly recognised prior to 1982 with small alluvial gold workings noted in several places but no evaluation or reporting undertaken on these occurrences. The islands were recognised as a new epithermal gold province with potential to host large Pleistocene to Recent gold deposits related to volcanism, major northeast trending rifts and west to north west trending, dome bounding fault zones and ultramafic rocks.
The four most important gold depositional zones are the Barrier Islands Rift / Graben, the Kukuia-Lavu Rift / Graben, the Oredi- Dei Dei Graben and the dome bounding faults that host the Wapolu Deposit on NW Fergusson and the Gameta Deposit on NE Fergusson. Structures which splay off the main rift / graben bounding faults are also important.
The key to success is the suitable gold depositional hosts, including faults, dome bounding shears, ultramafic rocks and breccia zones of various types.
The mineralised styles recognised as viable exploration targets include:
Descriptions of 21 prospects or gold/toxic element anomalous areas are listed below. Many have only had cursory, follow up exploration completed. Detailed re-evaluation of these prospective zones will be undertaken by Quintessential to rank follow up and drilling targets.
Sanaroa Island is prospective for a major disseminated gold deposit, being underlain by strongly advanced argillic altered and locally silicified Quaternary rhyolitic to andesitic volcanics with active hot springs in the eastern part of the island.
The Yaboa Hill hydrothermal breccia area has been geological mapped, bulldozer costeaned and had one diamond core and four rotary air blast holes drilled. Altered and sulphide bearing volcanics and some breccias were intersected in the trenches and the drill holes. The trench mapping suggests that the volcanics become increasingly altered and brecciated towards the south with zones of chalcedonic quartz veining and pyrite noted in one trench. This area returned several intercepts averaging better than 0.1 g/t gold, the highest being 0.44 g/t gold over 2.4m. Petrology from the drilling indicates an acid leach upper zone with a boiling zone beneath conducive for gold mineralisation.
The Bwaiya prospect is underlain by altered felsic volcanics which probably unconformably overlie gneissic granodiorite. Fresh andesitic volcanics have also been mapped within the prospect area and ultramafics have been noted to the east and west of the immediate prospect area.
Initial reconnaissance float sampling returned 2.89 g/t Gold showing potential for epithermal gold. Grid soil sampling substantiated earlier ridge and spur sampling results with many soil samples > 0.05 g/t Gold and a strong correlation with anomalous arsenic. Virtually all rock samples from Bwaiya contain greater than 100 ppm arsenic; the average for the 49 rock samples is 410 ppm arsenic.
The alteration present is described as consisting of silica flooding, clay development and vuggy cockscomb quartz veins in volcanics and granitic rocks. Fresh and partly oxidized pyrite is abundant throughout the altered volcanics. Nearby brecciated ultramafics show local zones of strong silicification with black opaline silica and fine disseminated pyrite.
Based on petrological studies, the felsic volcanics and older intrusives (granitic) are noted to have been subjected to at least two phases of alteration: (i) a high temperature, potassic alteration with peripheral phyllic and propylitic alteration, and (ii) a low temperature, epithermal argillic alteration consisting of interlayered illitic clays + quartz + adularia + calcite, which has overprinted the higher temperature mineralogy. Gold mineralisation occurs in both felsic volcanics and intrusives and appears associated with the later epithermal stage of alteration.
There is widespread epithermal alteration with anomalous gold and toxic elements in rock chip and Ridge and Spur soil samples associated with the NE trending Oredi Structure. Three diamond drill holes tested structurally controlled epithermal gold mineralisation hosted by brecciated and silicified ultramafics. The best grades include a 70m section of 0.50 g/t gold in drill hole ORD001; including several intervals over 1.0 g/t and a high of 3.32 g/t gold over 1.3m. There was anomalous arsenic, silver and nickel in some of the stream sediment samples.
Silicified ultramafics overlie metamorphics (gneiss) on a decollement fault surface. The ultramafics are strongly brecciated and silicified near the contact. Original ultramafic rocks were olivine dunite and pyroxenites. The metamorphics consist of quartzo-feldspathic leuco-gneisses and schists. These rocks are invaded by chalcedonic quartz-adularia veins near the contact and intruded by fine grained andesitic to basaltic dyke rocks. Alteration within the ultramafics is quite extensive and the thick soil colluvium cover has had a masking effect on the gold in soil results which is anomalous over a 2 km2 area.
At Bolu Bolu North, Motouya and South Prospects on eastern Goodenough Island, mineralisation occurs in a similar geological environment to the Wapolu Deposit and has been traced over a strike length of 7 km. The prospects lie on the NW trending and NE dipping Wakonai Fault. The footwall rocks consist of leucocratic and amphibolitic gneiss while the hanging-wall rocks consist of sheared and brecciated ultramafics. Locally, Pleistocene volcanics overlie the hanging-wall ultramafics as do thick colluvium deposits which are shedding from the footwall gneisses. Combined brecciation and silicification with variable pyritisation of the ultramafics occurs along the main fault zone and are accompanied by anomalous gold, arsenic and molybdenum values.
Results from bulldozer trenches at Bolubolu North include 39m of 2.10 g/t gold including 6m of 11.90 g/t gold (horizontal zone), and 8m of 4.90 g/t gold including 4m of 6.14 g/t gold, (vertical zone), 4m of 5.05 g/t gold, 5m of 1.540 g/t gold, and a float sample carrying 5.60 g/t gold and the highest rock being 24.70 g/t gold.
The BoluBolu South Prospect covers an area of strong silicification where sampling programs returned results such as 3.53 and 3.24 g/t gold in pan-concentrates, anomalous silt samples, rock float sample of 1.17 g/t gold and the best trench sample of 5m of 1.06 g/t gold. A large number of samples contained arsenic values greater than 1,000ppm to a maximum of 5,400ppm arsenic.
The Motouya Prospect is located between Bolu Bolu North and South Prospects and covers 4km x 1 km. Reconnaissance sampling returned 1.95 g/t gold in stream sediment and 1.78, 0.88 and 2.87 g/t gold in a rock float samples. A single soil anomaly of 0.668 g/t gold was noted.
This prospect occurs on a major NE structure which is evident as a magnetic low situated in the central part of the Kukuia-Lavu Graben, with recorded alluvial gold workings in the prospect area. Historical gold in pan concentrate samples returned 43.90, 26.0 and 18.0 g/t gold with correlating high arsenic, antimony and silver.
Follow-up drainage sampling provided gold values of up to 76.0 ppb bulk cyanide leach, up to 95.94 g/t in pan concentrates and up to 1.44 g/t in -80 mesh sediments. Ridge and Spur soil sampling at 25m intervals had no anomalous gold values. Rock chip sampling returned a high of 2.84 g/t gold. The High gold-in-pan concentrate sample appears to have been collected from an area underlain by the Omara Granodiorite.
This prospect was identified by anomalous pan concentrate and silt fraction gold assays, including 44.5 g/t gold pan concentrate (+0.270 g/t Gold silt) and 12.0 g/t gold pan concentrate (+1.28 g/t gold silt). Anomalous gold and arsenic in -#80 stream sediments is suggestive of epithermal vein mineralisation. Anomalous gold in Ridge and Spur soil samples occur over a 1.5 km2 area and 15.6 g/t gold, 10 g/t gold and 0.88 g/t gold rock samples were collected from a quartz vein over 120m in a creek.
This prospect is defined by a two panned concentrate stream samples of 1.89 and 2.67 g/t gold on the edge of a 2km x 1km volcanic extrusive, evident in the airborne magnetics image. Three stream sediment samples were collected within the boundaries of this prospect. In two of these visible gold was panned and they assay 1.89 g/t gold and 2.67 g/t gold respectively.
Fifteen rock float samples show high arsenic (to 1490 ppm) and antimony (to 100 ppm) values and one anomalous gold value of 0.18 g/t gold. The prospect area is underlain by strongly fractured and weathered ultramafic. Locally there are zones of chalcedonic silicification which appear to have an east to north-east trend and are apparently related to fault structures. These silicified zones can carry 5 to 10% disseminated pyrite. Granodiorite occurs immediately south of the prospect silicified zones.
This prospect is probably part of the same broad epithermal system as Bwaiya, with the host being ultramafic rock rather than volcanics. The high arsenic and antimony at surface suggests that the present surface is high in the epithermal system. Gold, if present, would occur at an unknown depth below surface.
This prospect is based on one float sample of altered felsic volcanics which contained 0.712 g/t gold, 1400 ppm arsenic and 100ppm antimony. One stream sample taken upstream from the float recorded 0.007 g/t gold. The regional geology of the area is mapped as granodiorite and gneissic granodiorite with ultramafic xenoliths, however the occurrence of the altered and mineralized volcanic float indicates the presence of volcanics in the area. South Boselewa s located about 2 kilometres south of Boselewa prospect and two kilometres southeast of the Bwaiya prospect.
Strongly anomalous arsenic, mercury and antimony cover 1km2 of brecciated ultramafic with variable silicification, opaline veining and pyrite-arsenopyrite mineralisation. The structural preparation, silicification, veining and high trace element geochemistry are all positive indications for a possible gold zone at depth.
Reconnaissance sampling returned low stream sediment and low panned concentrate results, with 0.015 g/t Gold and 0.023 g/t Gold, respectively. Out of the 32 samples collected, two rocks contained appreciable gold with 0.057 and 0.291 g/t gold and 13 had over 1,000 ppm arsenic (peak = 1.24%), between 50 and 181 ppm antimony and mercury to 17.4 ppm. Highest values from 32 samples included 0.057 and 0.291 g/t gold. Trace element geochemistry (As, Hg), veining and silicification indicate a possible gold zone at depth.
Moderately auriferous quartz veins are interpreted to be structurally controlled along the NE transfer fault zone. A high value of 1.4 g/t gold was received from a quartz boulder. Basement gneisses are cut by 10-20cm thick mesothermal quartz veins with pyrite and galena. Results from panned stream sediment concentrate include 1.34 g/t gold, 1.23 g/t gold, 1.14 g/t gold, 1.29 g/t gold, 1.2 g/t gold and 0.76 g/t gold over a 3 km2 area.
This area has a 15 to 20m wide shear zone with highly silicified and pyritic clasts with a rock chip sample containing 200.0 g/t silver. Channel and float rock samples collected were generally below 0.20 g/t gold and up to 75 g/t silver. There is anomalous zinc and copper up to 0.13% copper in the rock samples over a 1.3km by 300m area.
The geology of the prospect consists of lower gneiss which contains occasional 10 to 20cm wide metamorphic quartz veins overlain by up to 100 meters of ultramafic which is fractured and oxidized.
Exploration discovered highly silicified, serpentinised and brecciated ultramafics overlying gneissic basement. The contact is strongly sheared and the intensity of alteration and silicification seems strongest near the contact. The Pagalolo prospect may be the southern extension of the Oredi Creek Prospect. Gold and toxic elements are weakly anomalous. Highest assay values from stream samples and rock chip samples were 0.05 g/t gold, 0.7 ppm silver, 250 ppm zinc, 1830 ppm arsnic and 60 ppm antimony over a 0.5 km2 area.
The Gauyasi prospect is on a major structural trend known to contain gold mineralisation at Laimomo and Wapolu and the faulting in the area is complex (enhancing the areas' prospectivity). A pan concentrate sample from a creek ran 0.3 g/t gold. A soil grid was put in but the area of interest was not entirely covered. A soil sample returned 2.58 g/t gold and a re-assay of 2.91 g/t gold and is located 25m from the SE grid boundary.