High grade massive sulphides discovered on Romang Island: Robust

By Ruli Setiawan

ASX-listed Robust Resources Limited announced Tuesday that a new discovery of high-grade massive sulphide mineralization has been made beneath the existing Batu Mas JORC (2004) Mineral Resource area at its Romang Island gold project in Indonesia. The new discovery and mineralized domain is called Batu Mas Deeps prospect.

The company said in a statement that diamond drill hole LWD 352 has intersected one of the most significant zones of mineralization yet to be encountered at the Romang Island gold project.

LWD 352 intersected a broad zone of polymetallic mineralization over 100 meters thick that contains a 6 meters zone of very high grade massive sulphides. The intersections include:
o 102.8m at 5.71% combined base metals and 0.40 g/t AuEq from 110m
(0.19% Cu, 2.54% Pb, 2.99% Zn, 0.13 g/t Au, 14 g/t Ag) including massive sulphides:
o 17.0m at 25.67% combined base metals and 1.07 g/t AuEq from 175m
(0.86% Cu, 11.97% Pb, 12.84% Zn, 0.14 g/t Au, 49 g/t Ag) including:
o 6.0m at 54.90% combined base metals and 1.78 g/t AuEq from 176m
(1.48% Cu, 26.02% Pb, 27.40% Zn, 0.16 g/t Au, 49 g/t Ag)

LWD 352 was terminated for technical reasons whilst still in strong mineralization (>3% base metals) so it is likely that the mineralization is even thicker than has been obtained in the drilling.

The mineralization in LWD 352 is a down-dip extension of a mineralized zone in LWD 120, completed 2 years ago, with assay results announced on 11 October 2011. At the time LWD 120 was recognized as an intersection having significant potential but follow up drilling was deferred whilst all available drilling resources were directed towards shallow oxide gold-silver targets. Intersection in LWD 120 include:
o 53m at 9.52% combined base metals and 0.64 g/t AuEq from 123m
(0.62% Cu, 4.40% Pb, 4.50% Zn, 0.11 g/t Au, 26 g/t Ag) including massive sulphides:
o 22.0m at 21.63% combined base metals and 1.22 g/t AuEq from 134m
(1.36% Cu, 10.03% Pb, 10.24% Zn, 0.14 g/t Au, 57 g/t Ag) including:
o 10.0m at 27.77% combined base metals and 1.30 g/t AuEq from 176m
(2.36% Cu, 8.65% Pb, 16.76% Zn, 0.16 g/t Au, 61 g/t Ag)

The grades of the Batu Mas Deeps massive sulphide mineralisation from LWD 120 and LWD 352 compare favorably with historical, current and proposed high-grade underground lead-zinc-silver and polymetallic deposits elsewhere, Robust Resources said.

Some examples of the grades reported for this type underground mine/deposit are:
? The famous Broken Hill South underground mine in Australia produced 34 million tonnes of ore grading 25.5% combined base metals and 230 g/t Ag to a depth of 1.7 Km before it closed in 1992.
? Rosebery is an underground VMS mine in Tasmania has been operating since 1893. In 2004 it was producing with mineral reserves of 5.3 million tons at 15.7% combined base metals, 1.7 g/t Au and 123 g/t Ag. It remains operational to this day.
? The undeveloped Anjing Hitam deposit in Sumatra, Indonesia is considered to be an attractive underground mining and development proposition. It has a mineral resource (2004) of 7.7 Mt at 25.8% combined base metals and 12 g/t Ag.

The reason for this comparison of grades is that if the Batu Mas Deeps exploration is successful in delineating even a modest tonnage at or near to the grades obtained so far, then early development and extraction by underground mining of high-grade ore might be an option to enhance the economics of the Lakuwahi project as a whole, the company explained.

It should be noted that it was the discovery of the high-grade Zone VII at the Porgera Mine in PNG that transformed the economics of that project. Zone VII was mined first from underground and then a large open pit extracted the adjacent lower grade ore. This underground mine was highly profitable and funded much of the development capital for subsequent open pit mining.

It should be noted that for Batu Mas Deeps there has been insufficient exploration to estimate a mineral resource and there remains uncertainty that further exploration will result in the estimation of a mineral resource. Robust is now prioritizing drilling the Batu Mas Deeps domain using two dedicated diamond drill rigs.

Robust?s Managing Director Gary Lewis commented: ?Romang Island is now living up to its promise of becoming a world-class polymetallic deposit. The results from LWD 352 are exceptional and appear to show a trend towards higher-grade massive sulphides with increasing depth. Deeper drilling is now unlocking the full potential of Romang Island and Robust is committed to defining the full extent of the mineralization of the Lakuwahi Caldera and other targets on Romang Island.

Editing by Reiner Simanjuntak