In Kazakhstan, gold-mining has occurred since Stone Age times (with the earliest open-pit ‘workings’ dated to 4,000 B.C); and numerous underground mines began cropping up during the Bronze Age (1,500 BC). These deposits were later forgotten; that is, until antiquity gave way to modernity, - with most rich gold deposits found in Kazakhstan (during the prolific 1920s and 1930s) actually ‘re-discoveries’; sites disclosed with the help of ancient folk tradition, on the basis of old place-names (meaning ‘gold’), or through the whereabouts of shafts, pits and quarries. In just such a fashion, the Zhanatobe deposit was ‘rediscovered’ in 1932.
After underground mining in the 1940's (by a small mining cooperative), systematic exploration of this deposit was conducted in 1950-1951, to be followed by full scale mining (through the state owned Stepnyak mining company) until 1981; with the mine eventually consisting of 3 shafts and several drifts reaching the depth of 50 meters below the surface.
Alhambra began its exploration of the area in 2006-2008, commencing with soil sampling from an area of 5.5 square kilometers (around the known deposit); then, in 2009, it expanded the area of investigation (with soil sampling) to an area of 77.7 square kilometers. Moreover, for a part of that area, geological mapping accompanied by rock chip sampling was conducted (1,877 samples were taken); outlining two zones with a high density of anomalous gold concentrations (above 70 parts per billion gold ("ppb Au")) in volcano-sediment rocks.
Around this period, geological mapping demonstrated the gold anomalies to be controlled by a NNE orientated district scale shear zone and its NW striking splays; and there were several clusters of higher (+0.1 grams per tonne gold ("g/t Au")) gold concentrations in rock chip samples inside both anomalous zones. They manifested the following dimensions and peak gold grade concentrations:
• Northern Area (cluster) - 3.3 kms by 0.8 kms with the highest grade of 34.4 g/t Au;
• Central Area - 3.7 kms by 2.5 kms, up to 11.5 g/t Au;
• Western Area - 1.3 kms by 0.7 kms, up to 2.0 g/t Au;
• Eastern Area - 5.3 kms by 1.2 kms, up to 6.3 g/t Au;
• Southern Area - 6.0 kms by 3.1 kms, up to 5.1 g/t Au;
Given such research, it was possible to discern that the main zone had a NNE orientation (about 15.8 kilometers long and up to 5.8 kilometers wide, remaining open in both NNE and South Southwest directions) while a second zone trending NW to West Northwest was intruded by a granodiorite intrusion (with dimensions of approximately 7.7 by 1.2 kilometers). Anomalous gold grades in both zones (supported by elevated silver) suggested that mineralization is just slightly eroded and could continue to a significant depth and there are several clusters of higher (+0.1 g/t Au) grade rock chip samples inside both anomalous zones.
At this stage, the Northern and Central Areas looked to be the most “prospective”, for, in tests, the Northern and Central areas demonstrated not only high peak grades (34.4 g/t and 11.5 g/t Au respectively, reported previously) but also consistent spatial distribution of the rock samples grading more than 0.1 g/t Au. Specifically, the Northern Area (3.3 kilometers by 0.8 kilometers), including the old Zhanatobe mine, had produced rock samples containing high gold concentration covering a wide territory; being related to sets of quartz veins and silicified zones. And, for its part, the Central Area (3.7 kilometers by 2.5 kilometers) appeared to be even more promising; for here, the gold-silver mineralization was related to zones of silicification (some of them up to 520 meters wide and 180 meters long).
From an exploration perspective, something arousing a great deal of interest had turned up, for fragments of opaline-jarosite and jasperoid style silicification zones (in brecciated calcareous sediments) looking similar to Carlin-style collapse breccias were mapped in the Central Area, - indicating the potential presence of epithermal style gold mineralization; a style not recognized in the license before. And, yes, the previously mentioned higher silver values very much supported this scenario.
As 2009 came to a close, (with growing excitement) the drilling campaign for 2010 was devised to establish grade consistency and further refine (the shape and size of) the gold mineralization. Needless-to-say, considerable anticipation was building: would the Central Area’s Carlin-style collapse breccias prove to be significant or just an aberration; for, if they did prove out, this silicified zone would constitute a very attractive ‘prospect’; indeed.
During 2010, fifteen lines of RAB drilling (amounting to 483 drill holes totaling 4,744 meters) were completed in both the Northern and Central areas of Zhanatobe; and it appears that there is sediment hosted, fine grained disseminated gold, accompanied by de-calcification and brecciation, a spatial link to granitoid intrusions, strong silicification (expressed as jasperoid), the secondary mineral jarosite and, as indicated by the rock chip sampling program, high Ag and strongly elevated As and Sb. This is precisely what they were hoping for.
Well, - turns out, - the rotary air-blast ("RAB") drilling program carried out in 2010 resulted in the discovery of two possible "Carlin-style" zones of gold mineralization; - one in the Central area and a second in the Northern area. In fact, while the zone of gold mineralization discovered in the Central area is approximately 850 meters in length and 100 meters in width, (surprise, surprise!) the zone of gold mineralization discovered in the Northern area is approximately 400 meters in length and 150 meters in width (and open on both ends); prompting management to remark “which suggests that we may have located a new very large, prolific area of gold mineralization.”
And this, - “As a result, we anticipate implementing a more aggressive 2011 drilling program including deeper, more precise core drilling, with the objective of reclassifying Zhanatobe from early exploration status to advanced exploration status in 2012." This will consist of a sequenced drilling program with 856 RAB holes, 17 RC holes and 5 core holes that test other prospective areas of the project, determine the shape and size of the discovered zones of mineralization, prove the mineralization style, and most importantly, define gold grade at depth.
O.K., given that the Central Area’s zone (a new style) is interpreted to be related to the contact of a silicified body with sandstone, calcareous sandstone and epiclastic sandstone host rocks, and, furthermore, given that the Northern Area’s (new style) corresponds with a silicification and brecciation zone (at the contact between calcareous and epiclastic sandstone and siltstone horizons), this has lead Alhambra to believe that the two newly discovered zones of gold mineralization may be Carlin-style in nature, named after the Carlin Mine on the Carlin Trend in Nevada (USA). While Carlin-style gold mineralization has not been previously recognized in Northern Kazakhstan, it has generated a significant percentage of the world's gold production.
And, yes, this style of mineralization (exhibiting many similarities to "Carlin-style" gold mineralization) is completely new for the region.
As everyone already knows, the Carlin trend (discovered by Newmont geologists in 1961) forms the largest and most productive accumulation of gold deposits in North America; with a reported gold endowment (including past production, reserves, resources, and mineral inventory) exceeding 107 million ounces; consisting of more than 40 separate deposits. The Carlin trend is a 38-mile (60-kilometer) long north-northwest alignment of predominantly carbonate-hosted gold deposits (located in northeastern Nevada) where gold deposits are generally hosted in a variable stratigraphic package of Ordovician through Lower Mississippian rocks; where broad amplitude, northerly plunging anticlines within autochthonous carbonate assemblage rocks have been preserved in uplifted ‘tectonic windows’ along the Carlin trend, and all Carlin trend gold deposits discovered thus far occur within or proximal to these tectonic windows.
The north-northwest alignment of the Carlin trend deposits is not in itself a manifestation of any singular fault zone, but rather a combination of structural features in a zone of crustal weakness and sustained high heat flow, as indicated by multiple periods of intrusive activity (with this environment creating a setting conducive to prolific gold mineralization).
The extent of silicification differs between types of deposits and, similar to carbonate removal, its importance as an alteration product is partially controlled by the composition of host rock. In the Carlin deposit, early stage acidic hydrothermal fluids have evolved into thermal equilibrium through a process of groundwater mixing. In this restricted model, silica continued to remain in equilibrium until the late-ore to post-ore stages of the hydrothermal system; and was then precipitated as pressure-temperature conditions waned. These relationships suggest an early stage of silica and base metal deposition occurred in more passive, strata-controlled gold deposits. Gold in the Carlin trend deposits occurs as submicron particles (50–200Å) primarily within the lattices of pyrite and arsenian pyrite; with fluid inclusion studies suggesting that gold was transported as a hydrogen bisulfide complex.
Carlin trend geologists have identified three components as being necessary for the formation of this ‘style’ of gold deposit: strength of the hydrothermal system, structure, and host rock. Within this context, those major geologic parameters that have contributed to the genesis of gold deposition on the Carlin trend include: (1) reactive and highly permeable carbonate host rocks; (2) a geologically long-active zone of crustal weakness originating along a paleo-continental margin, with development of major through-going fault systems; and (3) a regional tectonic environment of crustal thinning, with multiple intrusive episodes and sustained high levels of heat flow, which resulted in (4) multiple episodes of hydrothermal activity.
According to one of the world’s leading experts on this trend, Professor David Groves, the relative importance of stratigraphic and structural controls to gold deposits has been recognized by numerous workers on the Carlin trend (Groves, 1996).
By the way, after carefully reviewing Alhambra’s geology, projects, and prospects, Dr. Groves recently concluded that the area is “very prospective” and “in elephant country” and that “current targets may not be primary targets”; concluding: “expect numerous world class deposits in this area“.
… ….. Is this the kind of thing he had in mind?