EXPLORATION ROUNDUP — Atapa puts Indonesian gold projects on fast track

By focusing on past-producing properties, Toronto-based junior Atapa Minerals (ATAP-C) has secured itself as one of the leaders in Indonesia’s exploration play.

The company is exploring the 101,400-ha Cikotok mining permit in West Java — together with joint-venture partner Aneka Tambang, the state-owned mining company — and is completing a deal to acquire a minimum 51% interest in the property.

Atapa believes Cikotok has the potential to host large-tonnage, low-grade, disseminated, epithermal, quartz stockwork, porphyry and carbonate-hosted gold systems. Two past-producing mines on the property, Cikotok and Cirotan, produced in the order of 8 tons of gold, 185 tons of silver, 4,000 tons of lead and 5,000 tons of zinc concentrates.

Secure in its belief, the company has been conducting an aggressive exploration program of diamond drilling, geological mapping, trenching and regional exploration to cover the property’s several gold prospects and 18-25 known gold showings.

The Cikidang prospect, formerly mined by Aneka Tambang, represents Atapa’s most advanced project. Situated in a 2.4-sq.-km alteration zone, the main Cikidang quartz vein was previously calculated to host 473,000 tonnes grading 10 grams gold and 87.7 grams silver per tonne. Atapa, however, believes these numbers offer little insight into Cikidang’s true potential.

“Aneka Tambang was looking for the high-grade section of the quartz vein, and that’s all they were interested in taking out,” says Atapa President Scott Keevil. “What they wanted to do was keep their 200-tonne-per-day mill going and basically keep their existing workers employed.”

The main vein has a north-south strike length of 1.2 km and averages 1.5 metres in width. Recorded grades are in the order of 54.4 grams gold and 116 grams silver. The vein lies in the western end of an unexplored, 1.5-by-1.6-km, prophylitic-argillic alteration zone and is open along strike in both directions. Initial surface exploration has identified similar-sized quartz veins branching to the east and west.

The vein is being developed by Aneka Tambang, which has so far completed three levels of drifting to a maximum vertical depth of 70 metres. As well, several crosscuts and raises have been driven. A fourth drift is being driven along the vein’s northern extent.

Existing reserves take into account only the high-grade vein, leaving out the smaller quartz veins, fractures and shatter zones. Many of the crosscuts have returned several metres of low-grade material. One of the more impressive cuts returned 15 metres grading 5.87 grams gold and 28.46 grams silver, including 7 metres grading 12.5 grams gold and 56.14 grams silver. Atapa says these numbers indicate the prospect’s true potential.

In addition, the junior notes that Aneka Tambang sampled only drill core that intersected the main vein.

In order to test its theory, Atapa began to re-log and re-assay all available drill core; it also undertook to sample all surface and underground outcrops.

Initital findings indicate potential average widths of up to 10 metres with gold grades in the neighborhood of 7 grams.

In the first quarter of 1997, the company will launch an initial, 5,000-metre program of subhorizontal, underground drilling in an effort to test mineralization on the vein and in the surrounding host rocks. A separate, 9,000-metre program of surface drilling, spaced at 40-metre centres, will test the vein to a vertical depth of 150 metres.

If results prove encouraging, the company will undertake a prefeasibility study within the next 18 months.

Meanwhile, on the Pasir Ela and Pasir Keris targets, about 6 km southwest of the Cikidang prospect, Atapa is attempting to develop a bulk-minable deposit.

The two targets comprise one prospect, also called Pasir Ela, which is underlain by a large alteration zone where numerous quartz veins and quartz-vein stockworks are hosted by intensely argillized and silicified volcanic rocks.

Pasir Ela target

The Pasir Ela target, a 600-by-400-metre area, consists of argillic alteration and quartz vein stockworks in two prominent, northeast- and northwest-trending vein sets. Trenching in the area returned 16 metres grading 2.51 grams gold. Also, channel sampling returned 5 metres grading 9.19 grams gold from outcrops in the vicinity of a hole, drilled by Aneka Tambang, that averaged 0.63 gram gold and 24 grams silver over 195.1 metres.

To date, Atapa has completed 740 metres of drilling, highlights of which include 7 metres grading 2.05 grams gold and 23 grams silver. Recently, an additional rig was mobilized to the area in order to drill deeper holes but, owing to rainy weather, had to be shut down.

At the Pasir Keris target, 1.5 km southwest of Pasir Ela, Atapa has completed 2,000 metres of diamond drilling. The target area is a large zone of argillic alteration with moderate quartz-pyrite stockwork and sheeted veining. Several high-grade zones were intersected, including 100 grams gold over 1 metre.

Petrological studies of Pasir Keris drill core indicate the area to be a multi-phase alteration system related to intrusive activity. Pending further petrological studies and surface re-evaluation, the company will resume exploration work with an emphasis on porphyry-style copper-gold mineralization.

The company has started a 2-month compilation program and intends to embark on a program of geophysics, combined with 4,000 metres of diamond drilling, by early March. The work will be aimed at developing a bulk-minable, open-pit operation.

Meanwhile, at the Cirotan prospect, 5 km to the north, Atapa has completed 2,000 metres of diamond drilling in an effort to test the hangingwall and footwall structures encompassing the past-producing Cirotan mine.

Of the six holes drilled, five intersected the Main zone. Hole 4 intersected 20 metres grading 2.07 grams gold and 119 grams silver, including 5 metres of 4.78 grams gold and 99 grams silver.

Gold mineralization in the area occurs in quartz-sulphide veins within a 20-metre-wide breccia zone that dips 60 to the east. The structure extends for at least 4 km along strike.

Breccia zone unexplored

The previous operator concentrated on a high-grade oreshoot, which plunges steeply to the north. Mining occurred on 10 levels over a vertical interval of 300 metres and an average mining width of 5 metres. Atapa believes the area has good potential for containing a significant gold resource, as only the high-grade material (exceeding 6 grams gold) was mined, while the mineralized breccia zone was ignored.

In addition to other prospects, the company is exploring several gold showings in the Cikotok mining permit. Original regional exploration programs were aimed at finding quartz-vein, epithermal gold systems. However, preliminary geological mapping and outcrop sampling in the northwestern portion of the property have influenced the company’s exploration strategy, and Carlin-type systems are now being sought.

“Since we’ve done some regional exploration on the western part of the property, everyone is now enthusiastic that we are looking at a Carlin trend-type setup, with jasperoids and sediment-hosted gold mineralization,” says Allan Hawke, vice-president of exploration. “This coming year, we intend to focus a lot of attention on that particular model.”

Recent work in the area led to the discovery of a 3-sq.-km area of silicified, altered limestone and sediments. Samples returned up to 1.6 grams gold and 34 grams silver per tonne.

Atapa expects to spend $9-10 million next year at Cikotok, half of which will be allocated to the Cikidang prospect.

On the neighboring island of Sumatra, Atapa plans to enter into an joint venture with Stroud Resources (SDR-T) to explore three properties, totalling 44,300 ha, in the Lampung province. Once the deal is made final, Stroud will assume operatorship and earn a half interest in the joint venture.

Previous work on the properties is limited, but stream-sediment gold anomalies and gold showings from workings are reported. Atapa says the area has potential for both epithermal and intrusive-related gold deposits.