BATAK your Land is Rich of precious mineral dont forget to share with the World.

TO all new generation especially student ..please note…

Lets enjoy our wealth to support our future.welcome all foreign investor But remember…sign an international agrement about land right or royalty to the traditional batak owner right.its not mining right.ok?

on the other hands please carefull with all dirty politician in locally or from jakarta. do not let them play their dirty game…using old young uneducated people to stir up the problems for their purpose to get bribes money and ignored the royalty from the company and local/central goverment.jakarta/indonesia.

Look at the toba pulp…bribes money gone to the local authority and gangster but left the polution and unpaid royalty to the local land owner and destroyed all the land scape ..just for making few people billioner form the company.

Good luck my batak people and be nice and become a good community to the world.Horas by roy_sianipar

Regional Geology
The basement rocks of northern Sumatra are the Permo-Carboniferous age Tapanuli Group, generally sub-divided into the poorly constrained flysch dominated Kluet Formation and the overlying (?) shelf carbonate Alas Formation (Aldis et al 1983). In the northern part of the CoW this relationship is apparent while in the Sopokomil district it is not possible to strictly assign the rocks to either and so the local term “Silima Pungga Pungga Formation” is applied and this can be locally sub-divided into several members, all carbonate bearing to a greater or lesser degree. They are relatively weakly metamorphosed but often quite strongly tectonised.

The Tapanuli Group rocks are affected by several deformation events – firstly in the Permian (op cit) and one or more in the Mesozoic, with accompanying granite intrusion (Cretaceous?), observable about 10km south of Sopokomil. The major deformation of the Tapanuli Group occurred in the Neogene with the formation of the Barisan Geanticline (op cit) and the Sumatran Fault System (SFS), which runs NW-SE along most of the length of Sumatra. This has variable dextral transcurrent to vertical movement. Most fold axes in the Dairi region parallel this and SW vergence is apparent in the Sopokomil Dome.

Adjacent to the SFS is the Lake Toba caldera from which the cataclysmic eruption of ignimbritic Toba Tuff occurred in the late Pleistocene, burying much of the rugged Barisan topography and covering up to 20,000 km2 area (op cit). The NE catchments draining the Sopokomil district are buried to ~650m ASL.

The Sopokomil Dome exposed sequence of Tapanuli Group rocks comprises an upper, monotonous dolo-argillite/arenite bedded sequence, termed the Dagang Member (see Table 1). This is transitional from the Julu Member – at the top “pinstripe” inter-laminated carbonaceous shales and dolosiltstones and containing the “Julu Sedex Zone” series of massive sulphide horizons, and in the lower part grading into bedded carbonaceous, dolomitic siltstones, becoming progressively more dolomitised

There is a sharp contact with a shelf carbonate sequence – collectively termed the Jehe Member, and essentially massive, fine grained dolostone with no observed fossils but an argillitic septum. The Sopokomil Member contains rare solitary corals and possible algal growths. Erratic carbonate matrixed quartz arenite facies intersected in drillholes may represent sinuous channels.

On the SW flank of the dome, and close to the near-surface manifestation of a strong magnetic basement, is some float of a magnetite bearing quartzose lithology which may conceivably be a skarn. This is termed the Dang Takkas Formation but its relationship with the other rocks is not clear.

The Sopokomil Dome is about 4.5km long between the closure of the Julu Member (Figure 1). It is aligned NW-SE, with SW vergence and a sense of overturning. It appears to be affected by an axis-parallel steep reverse fault system which causes repetition of the Julu Member.

Dips on the NE flank (most understood) range from 30-60°. There appear to have been three ductile deformation events and a late brittle deformation (Marjoribanks, 1999).

Elsewhere in the CoW there is a moderately open axial fold system trending NW-SE although most observed dips are to the NE. The main strand of the Sumatran Fault System (Renun-Toro) in this vicinity controls the course of the river Lae Renun while a WNW splay controls Lae Simbelin.


Julu Sedex Zone
This is traceable within the Julu Member from scattered outcrops in creek beds, soil geochemical anomalism and geophysical surveys, together with a scattering of drillholes around almost 5km of strike on the NE flank of the Sopokomil Dome. The main heliborne EM conductive zones are superimposed on geology in Figure 1. The zone varies in character from a single thick horizon, termed the Main Mineral Horizon (MMH), at Anjing Hitam in the far SE, to a thickness of up to 100m with multiple, mostly thinner horizons in the NW. Facies variation appears responsible with more quiescent local basinal conditions at Anjing Hitam while more carbonate-rich detritus is present in the NW indicating more rapid deposition off the dolostone shelf.

The mineralisation in the sulphide horizons is commonly laminated, exhibits apparent graded bedding in places, soft-sediment deformation of shale interlaminae etc, but has been overprinted by possible successive early diagenetic stage mineral pulses and several deformation events, including late hydrothermal and tectonic modification. There is a pyrite rich “proto-ore” type which is particularly fine grained, often well laminated and comprising 50-60% pyrite, 20-30% sphalerite, 10-20% galena with minor fragmental shale, quartz and barite. In polished section, discrete pyrite anhedra in the 50m range are set in a sphalerite-galena intergrowing matrix. There are commonly coarser grained, remobilised, brecciated, recemented sphalerite-galena rich sections with more shale fragments and only 5-10% pyrite. There are no other sulphide minerals in evidence.

Carbonate Hosted Mineralisation
Three main types occur in the Jehe Carbonate member :

1) Jehe Vein Type – a brittle fracture filling quartz vein system mostly restricted to the upper 20m or so of the Jehe and not extending up into the Julu; contains coarse sphalerite-galena-pyrite-tetrahedrite/tennantite, the latter quite silver-rich with drill intercepts to 5m @ 2.5% Zn, 4.6% Pb, 92g/t Ag.

2) Jehe Mississippi Valley Type –variably through the member with two styles – a shrinkage/slumping breccia cementing sphalerite-carbonate +/- pyrite in up to 30m thick zones of >1% Zn, eg 28m @ 3.1% Zn, 0.02% Pb, 4g/t Ag; also a matrix replacement style in carbonate matrixed quartz arenite with sp>py>>ga and drill intercepts to 10m @ 7.5%Zn, 0.5% Pb, 10g/t Ag.

3) Basuki Lode Type – occasional rubbly outcrop and creek exposures of brecciated, ferruginised material with erratic high grade zinc oxide (smithsonite + hemimorphite) and lead oxide (cerussite) mineralisation with drill intercepts to 10m @ 6.3% Zn, 6.5% Pb, 149g/t Ag. This type presumed to be recent karst deposited type from descending metal rich solutions derived from weathering JSZ.

It is significant that several lead isotope studies of the different JSZ massive sulphides versus Jehe carbonate hosted types indicate that the “sedex” form a distinct population (206Pb/204Pb<19.1 vs >19.1 for Jehe) which appears to be older than the more radiogenic carbonate hosted sulphide types (McInnes, 2001).

Anjing Hitam Deposit
This deposit at this stage appears to be fairly well constrained and comprises a “Main Mineral Horizon” of about 750m strike length, aligned NW-SE, average 250m dip extent, 12m average thickness, dipping 40-45°to the NE, shallowly plunging @ 15° to the SE, with a discontinuous “Upper Mineral Horizon” 5-20m in the hanging wall. The latter is affected by a bedding/layer parallel hanging wall shear.

Resource estimation is based on a block model constructed from wireframing of cross-sections. The blocks are mostly 25m x 5m x 2m thick. Grade and SG interpolation has been carried out using inverse distance cubed using Surpac software. A lower cut of 5% zinc equivalent is used for the sedex mineralisation and no upper cut has been applied. Exercises using nominal cutoff have been applied to some of the sparsely drilled carbonate hosted zones. Current resources are tabulated below and are considered compliant with JORC guidelines.

The “mining inventory” is derived from the mining scheme applied to the Anjing Hitam measured and indicated resource block model. It is 6.323Mt @ 16.0% Zn, 9.9% Pb or 21.5% Zn equivalent.

Figure 2

Anjing Hitam Plan and Cross-section 9900N

Table 2

Sopokomil Resources

Resource Category



Zinc Equiv.



Anjing Hitam JSZ
Measured & Indicated

Anjing Hitam JSZ

Basecamp JSZ

Lae Jehe JSZ



Acknowledgement is given to Dave Edwards, the original discoverer of the massive sulphide outcrops, to Rob Seed, the original site senior geologist who carried out much of the mapping and interpretation, his successor Ian Bruce and to Bernie Kirkpatrick for successive resource estimations. Also to our hard working Indonesian geologists: Anton, Sapto, Basuki and Herry and admin staff, especially Emmy and to Lorraine in Perth office for patient and constructive “IT”. Finally to the Board of Herald Resources Ltd for keeping the faith and to Drs M Tumanggor, Bupati (Regent) of Dairi for ongoing encouragement.

Aldis, D.T., Whandoyo, R., 1983, The Geology of the Sidikalang Quadrangle, Sumatra.

Sjaefudian, A.G., KusjonoGeological Research & Development Centre, Indonesia.

Bemmelen, R.W. van, 1970, The Geology of Indonesia, 2nd Edition. Martinus-Nijhoff, The Hague.

Lydon, J.W., 1995, Sedimentary Exhalative Sulphides (Sedex); in Geology of Canadian Mineral Deposit Types, Geology of Canada, Vol 8

Geological Survey of Canada.

MacInnes, B.I.A., 2001, Dairi Pb Isotope Data.Unpublished Memo from CSIRO Exploration & Mining to PT DPM.

Marjoribanks, R., 1999, An Interpretation of the Geology and Mineralisation of the Sopokomil Zinc Prospect. Unpublished report to PT DPM.

Simanjuntak, A.P., 1992, Report on Exploration of the Sopokomil District, Kecamatan Silima Pungga-Pungga, Kabupaten Dairi. Unpublished report by PT Aneka Tambang.


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