Geology and mineralisation of the Mewet Vein, Jelai Gold Project ...

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PT GMT Indonesia Mewet Vein : Jelai Gold Project quartz. Overprinting acidic/silica enriched fluids partially replaced the carbonate with amorphous silica, leading to massive chalcedonic silica with patches of bladed calcite pseudomorphs, lattice infilled textures and crustiform-colloform banded quartz veining. Photograph 1. Sample of Mewet Vein material showing the distinct banded nature of the higher grade vein material. Massive carbonate cavity fill in JM018 has been partially replaced by chalcedonic silica with the zone proximal to the colloform-crustiform banded quartz + adularia vein being completely replaced to massive chalcedonic silica. The elevated pH conditions from the draw down of acid sulphate rich water lead to the deposition of adularia disseminations and as banding in the colloform-crustiform banded quartz. No zone of advanced argillic alteration has been noted in the Mewet Vein system or surrounds, indicating that the upper section (mixing zone) has been eroded down to the relative level of the boiling zone. Continued boiling of the epithermal system lead to several telescoping phases of overprinting events, representing varying degrees of pH and concentrations of silica + CO 2 . The system represents several phases of sealing and rebrecciation with several phases of clasts of colloformcrustiform quartz clasts observed in the chalcedonic quartz. Colloform banded quartz clasts formed as a product of an acidic fluid are observed within a matrix of carbonate. Drusy quartz is in places overprinted with rhombic calcite with the calcite rarely displaying a late drusy quartz coating. Clasts of earlier chalcedonic quartz are often observed within the massive appearing carbonate veining and the quartz veining is also often represented by several phases of sealing and cracking. The collapse of the hydrothermal system led to the draw-down of meteoric waters leading to the deposition of glassy crystalline quartz + calcite. Rarely amethystine quartz veining is noted as a late overprinting event associated with the late draw down event. High grade gold values were restricted to the finely laminated chalcedonic quartz-adulariasulphide veins. Variable high gold values were encountered in brecciated chalcedonic quartz vein with the grade being dependant on the frequency of chalcedonic-colloform banded quartz vein clasts within the breccia. Significant gold mineralisation is hosted in typical high grade, low sulphidation veins. Maximum gold values were obtained from finely laminated colloform-crustiform banded quartz-adularia veins with zones of multiphase brecciation of the colloform banded quartz and healing by chalcedonic quartz returning the highest values. Brecciation of the colloform banded quartz and subsequent additional deposition of chalcedonic quartz + adularia lead an upgrade of the gold grade. The mineralisation was tightly structurally controlled with there being no gold mineralisation disseminated in the footwall to the vein. Low grade gold values were obtained within the breccia column on the hanging wall to the quartz vein. Silver grades are sporadic with the most elevated value occurring with the high grade gold in the finely laminated, sulphidic quartz veins. Unaltered andesitic basalt dykes were intersected; these were un-mineralised and appear to predate mineralisation. Weak to moderate propylitic alteration occurs within the andesitic dykes, predominately as fracture coatings. 0065 JCM/GEO/2009.04 Page 24
PT GMT Indonesia Mewet Vein : Jelai Gold Project 8 8.1 EXPLORATION PT Jelai Cahaya Minerals Exploration The project remained inactive for a number of years after it was abandoned by Ivanhoe Mines Limited. It is believed that a local miner attempted to develop a shaft on the Mewet Vein and evidence of this remains with a number of decaying sacks of quartz vein material dumped at the collar of a shaft a few metres in depth on the vein outcrop. It is though that the extremely fine nature of the mineralisation did not allow the recovery of any gold from the samples and the development was abandoned. In 2006, JCM Minerals placed an application over the known gold occurrences and this was granted on the 1 st June 2007. The management of the company, under the advice of a number of consultants, embarked on an aggressive scout drilling programme aimed at outlining the near surface extent of the vein systems. This programme was aimed at persistence, rather than the desire to obtain high-grade results, as it was determined that the soil cover in the project area could hide the mineralised lodes and shallow drilling was the most effective method for delineation of deeper targets. The exploration work was conducted by JCM personnel with technical assistance from PT GMT Indonesia (exploration consultants). Four drill rigs operated at the Jelai Gold Project, two scout rigs of Jakro 175 class, capable of drilling to depths of 75 metres in BQ diameter core (45 metres NQ diameter) and two larger coring rigs, a Jakro 240 and a RB34. These latter rigs can drill deeper, with the RB34 capable of drilling 200 metres BQ diameter and the Jakro 240 can drill to 200 metres NQ. The drill hole location map for the Mewet vein area considered is shown in Figure 5. 0065 JCM/GEO/2009.04 Page 25
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Geology and mineralisation of the Mewet Vein, Jelai Gold Project ...

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