Bewani Mountains

PROJECT BACKGROUND

The Kilifas platinum Prospect was discovered relatively recently (April 1968) when Bill Babbington, a prospector employed by the Territory of Papua and New Guinea Government, recovered Pt and minor gold (Au) from creeks near Kilifas village on the Yenabu River. The Pt is locally high-grade, but erratic, and is restricted to a small area around Kilifas. Babbington’s prospecting indicated that alluvial Pt is not found in any other stream in the surrounding district, suggesting a rather localised discrete source for the precious metal.

CRA Exploration ("CRAE") and Kenneth McMahon & Partners Pty Ltd made early assessments of the alluvial potential of the Kilifas Pt Prospect. Black collected 37 panned concentrates around the Kilifas site and from tributaries of the Yenabu River upstream and downstream of Kilifas. He reported results as a count of the number of colours observed in each dish. Two dishes from the Yenabu River immediately upstream of Kilifas village contained ten colours of Pt. Only a single colour of Au was reported from one dish. CRAE concluded that the immediate source of the Pt was conglomerate interbedded in Pliocene sedimentary rocks exposed along the course of, and to the north of the Yenabu River. However, as they further noted, no Pt was recovered from the conglomerate.

The assessment by a mining engineer from Kenneth McMahon & Partners involved the sinking of eight pits in each of two areas held under dredging and sluicing claims by T.J. Ward near Kilifas village. None of the pits encountered bedrock and all had to be abandoned because of caving associated with the water table. Pt values were encountered in five of the eight pits, although values were considered to be disappointing.

Peter Lowenstein, a geologist of the Geological Survey of PNG, investigated a 2.5 km section of the Yenabu River in June – July 1974. His panning revealed that about 6–7 colours of Pt and 1–2 specks of Au per dish could be obtained at the base of the gravels where they overlie grooved and fissured soft mudstone. No values were noted from tributaries that joined the Yenabu River, suggesting:

• CRAE's observation that the immediate source of the Pt is conglomerates was untenable. Given the widespread distribution of conglomerate lenses within the sedimentary sequence, one would expect to recover colours of Pt from the tributaries.
• The ultimate source of Pt lies upstream in the Yenabu River.

Significantly, Lowenstein noted that:

“...better panning values were obtained from sections of the river in which the gravels contain a large number of boulders of ultramafic rock. Fine-grained magnetite and occasional pebbles of magnetite also occur at the base of the gravels.”

Brisa Minerals Pty Ltd in 1988 completed an assessment of a 10 km interval of the Yenabu River alluvials downstream of Kilifas (Table 1). Their results indicate:

• Detrital assemblage consists of PGE (Pt-Pd) + Au.
• Very high concentrations of Pt and Au, in particular, are present in the Yenabu River for a considerable distance downstream of Kilifas.

Brisa Minerals surrendered the Kilifas area without any further assessment work.

Lowenstein’s observation that the best panning results at Kilifas are associated with gravels with a significant content of ultramafic boulders and pebbles of magnetite clearly indicates that the ultimate source of the Pt in the Kilifas Pt prospect lies within the Torricelli Intrusive Complex. In support of this conclusion, David Power-Fardy noted that many of the alluvial Au occurrences in the Bewani-Torricelli Mountain region contain various amounts of magnetite, ilmenite and garnet, compatible with the observation that ultramafic and mafic rocks of the Torricelli Intrusive Complex are the ultimate source.

Sedimentary rocks, containing interbedded conglomerate units, form an extensive cover sequence surrounding basement mafic-ultramafic blocks such as those in the Kilifas Range (Bewani Mountains). If, as CRAE concluded, conglomerates are the immediate source for the alluvial Pt, it does not account for Babbington’s district-wide panning results that showed that alluvial Pt is restricted to the Kilifas site. Sedimentary rocks underlie the Yenabu River and its N tributaries (Fig 1). The southern tributaries of the river upstream of Kilifas village rise within mafic-ultramafic rocks of the Torricelli Intrusive Complex and are considered to be highly prospective.

PPM'S EXPLORATION

Anomalous results of rock and panned concentrate samples from PPM's reconnaissance work are compiled together in Tables 2 & 3 (also see Fig 1). The cut-off thresholds used are: 0.01 ppm for Au, Pt and Pd and 0.02% for Cu.

Six float samples and one outcrop grab sample contained > 0.10% Cu. Copper values ranged up to 0.38 %. The copper anomalous rocks include altered microdiorite/ microgabbro containing 5–15% pyrite with trace chalcocite, chalcopyrite and quartz veins, calc-silicate skarns and hydrothermal breccias with <10% pyrite. Only one sample, a magnetite skarn float, returned anomalous Au (> 0.10 ppm). The Cu and Au anomalous float is sourced from southwestern tributaries of the upper Yenabu River draining Kilifas Range (Wa, Fukumu, Sie, Mue Creeks and Yenabu headwaters). The presence of Cu and Au-bearing altered intrusive phases, hydrothermal breccia and skarn float indicates porphyry potential in this section of the Kilifas Range. Streams draining the southern side of this porphyry prospective area (Sam, Kue and yes) also contain altered diorite float and/or pannable Au anomalies. The Kilifas Range is a priority target for further exploration.

Six panned concentrate samples contained between 1.0–32.0 ppm Pt and/or Pd and two panned concentrates contained > 100 ppm Pt. Five panned concentrates returned between 1.0–16.0 ppm Au and two panned concentrates returned very high Au concentrations of 90.4 and 384 ppm. The highest readings were taken from Waisi Creek. The presence of an intrusive pipe may still be possible despite detail mapping failing to locate and outcropping intrusive near the confluence. Steeply dipping bedding planes and limonite veins (50–85°) may be evidence of a buried pipe.