Jiguata Project
The Jiguata Project is located about 150 km east-northeast of the city of Iquique in Region I of Chile.
Fig. 1 Location of the Jiguata Project.
In July 2010, Minera Catalina SA registered sixteen “pedimentos mineros” (Jiguata 1-16) in the Court of Pozo Almonte. A further three pedimentos (Jiguata 17-19) were registered in November 2010, bringing the total ground held to 5,600 hectares. The project lies at an elevation of between 4,600 and 4,700 m (~15,000 feet above sea level).
There is an area of blanket coverage to the west and northwest by Codelco and Xstrata over areas considered prospective for massive porphyry copper deposits. Antofagasta Minerals has a number of claims immediately to the west of Jiguata.
Fig. 2 The Jiguata 1-19 Concessions.
The area was held previously by Codelco. Several trenches and two RC borehole collars have been observed within the area.
Fig. 3 A panoramic view of the Jiguata area, looking north. The conical hill is capped with younger volcanics.
The Jiguata area consists of a series of Miocene-Pliocene andesites, lithic tuffs and volcanic breccias unconformably overlain by a series of younger volcanics which covers and obscures much of the underlying geology.
Satellite imagery shows the extent of widespread steam-heated alteration with chalcedony replacement, which is characteristic, if not typical, of high-sulphidation epithermal gold deposits.
Fig. 4 A satellite image of the Jiguata area showing the extensive area of alteration. The dark brown rocks are the younger volcanics overlying and masking the extensive alteration.
The alteration covers an area of some 20 km2 (4 km E-W & 5 km N-S) and is seen where younger volcanic cover rocks have been removed by erosion exposing the underlying altered volcanic rocks in the base of valleys.
Fig. 5 An oblique satellite view of the same area showing the cover of younger volcanics overlying the widespread epithermal alteration.
High-sulphidation epithermal gold deposits often show a pronounced vertical zonation which is recognisable in part at Jiguata. To assist with defining this zonation, in addition to the field observations during the geological mapping, a suite of 119 hand samples were collected for spectral analysis using a portable ASD-FieldSpec Pro FR spectrometer to identify alteration minerals.
In the topographically higher areas of the concession, particularly towards the East, a zone of steam-heated alteration up to 100 m thick, with kaolinite, alunite, native sulphur and opaline silica forms a pervasive chalcedony blanket, which is likely to define a palaeo water table. Some of this chalcedony may be due to lateral migration of silicic groundwater from a large strata-volcano 5 km to the north.
Below this assemblage, and with a more erratic distribution, occurrences of chalcedonic breccia with disseminated limonite with silicic and argillic alteration and local residual silica textures can be recognised within the main host rock - a permeable lithic tuff.
This lithic tuff (shown in light green in Fig. 7) outcrops over only 25 per cent of the claim block; its full extent is obscured by colluvium or the cover of younger volcanics and volcanoclastics.
In the centre of the Jiguata claim block, a series of sub-vertical structures with quartz-alunite alteration are seen in outcrop. These are commonly vuggy and occur at the lowest elevation of any of the outcrops in the block and represent the most deeply-eroded part of the system. The leached vuggy silica is cut by post-leaching breccia and younger veinlets. Smectite and illite were also identified amongst the alteration minerals in this area supporting the observations that this is part of the deeper and higher temperature portion of the system.
A relationship with the nearby stratavolcano 5 km to the north is postulated but the extent of the silicification up and down dip is unclear.
It is proposed that the Jiguata claim block represents the uppermost part of a high-sulphidation epithermal system which is developed at depth and exposed in a “window” in the younger volcanics and volcanoclastic cover. Consequently, any geochemical response (particularly of precious metals) is likely to be muted. Nevertheless, the presence of native sulphur, opaline and chalcedonic silica, quartz-alunite alteration, barite veining and anomalous geochemistry of other elements are indicative of presence a large epithermal system.
Fig. 6 A chalcedonic quartz vein outcrop at Jiguata looking northwest. The vein is 0.8 m wide and strikes at 310°. Country rock shows some evidence of stockworks.
Geochemical Sampling
A programme of geological mapping and geochemical sampling was completed over the claim block in late October-early November 2010 with a total of 148 samples being collected and analysed for a comprehensive suite of elements.
Fig. 7 A plan showing anomalous gold values in the base of the valley.
In general terms, the areas with the most anomalous geochemistry are associated with outcrop in topographic lows (Fig. 7). However, this is not the only controlling factor as there are extensive areas within the claim block with either little or no outcrop and/or thick colluvium.
The drainage system downstream from the two RC drillholes, although adjacent to the strongest anomalies, has thick colluvium overburden where no sampling could be undertaken.
There are four areas with anomalous results:
- The area around the RC drillholes and the upstream extension to this area. Area A displays anomalous Au, Ag, As, Ba, Mo, Sb, Bi, Se, Pb, Te and Hg. Values of up to 1,700 ppm Mo, 400 ppm As and 0.3 g/t Ag were recorded. It contains the main quartz-alunite veins structures and is the most deeply eroded. The currently-known extent of these structures with their anomalous geochemistry is a function of exposure, colluvium and topography. The zone of interest is open to in all directions.
- A NE-trending valley approximately 1.5 km to the NW of the RC drillholes. This area proved anomalous Sb, Bi, Mo and Pb.
- A WSW-trending valley lying approximately 1 km E and S of the RC drillholes. It displays anomalous Sb, Ba, Te, Se, Ag and Hg.
- The extreme north of the property near to where the drainage system that passes through Area A meets the Lirima-Colchane road. It displays anomalous As, Ba, Te and Se.
From the geochemical anomalies described above, it appears that:
- Areas B, C & D are distinctly different.
- The only anomalous gold values are in Area A - the most deeply eroded part of the system.
- Mercury has a broader distribution than the other elements and anomalous values are seen both in Area A and over a much wider area of Area C than defined by other elements. Area B appears to be deficient in Hg. There are no anomalous Hg values in the northern areas where native sulphur is present.
Observations
At Jiguata alteration characteristic, if not typical, of high-sulphidation epithermal deposits is developed over an area measuring 5 km N-S and 4 km E-W.
The area is not well exposed. Colluvium, a cover of younger volcanics and volcanoclastics and the steam-heated cap provide an almost complete cover and the most interesting outcrops are only found in the base of valleys.
Consequently, although the area of alteration is extensive there is no guarantee that the area above the most promising targets at depth has been exposed. The best targets may lie in zones covered by colluvium and younger volcanics.
The area displays distinctly anomalous geochemistry although as expected the values returned are muted due to the incomplete exposure of the system.
Follow-up work programmes are now being planned with more detailed mapping and geochemical sampling in areas of interest where anomalies have been identified, extending that work to remote areas which have not yet been visited.
A geophysical survey (IP and/or MT) will follow in order to identify targets for a subsequent drilling programme. Quotations for this work are presently being sought from specialist contract companies in Chile.
In July 2011 Mariana Resources Limited, an AIM and TSX quoted exploration and development company focused on Argentina and Chile, entered into an Option-to-Purchase Agreement with Catalina to acquire a 100% interest in the 5,600 ha Jiguata property.
