The operating company Empresa Mixta Ecosocialista Siembra Minera, S.A., which holds the rights to the Siembra Minera Project, is a mixed capital company with 55% is beneficially owned by a Venezuelan state entity Corporación Venezolana de Minería, and 45% is beneficially owned by Gold Reserve Inc.
Summary:
The Project is a combination of the Brisas and Cristinas properties into a single project now called the Siembra Minera Project.
The Siembra Minera deposit lies within a portion of the lower Caballape Formation volcanic and volcanic-related sedimentary rocks. The units present are (1) andesitic to rhyolitic tuffaceous volcanic beds, (2) related sedimentary beds, and (3) a tonalitic intrusive body. All rocks have been tilted and subjected to lower greenschist facies metamorphism. It is thought, based on information from nearby properties, that the Siembra Minera Project occupies one limb of a large regional fold. Limited direction-indicating structures show the strata to be top-up. In the main mineralized trend, moderate to strong foliation is oriented N10°E and dipping 30° to 55° northwest. This foliation appears to be parallel to the original bedding and tends to be strongest in the finer-grained rocks. A much weaker foliation orientation appears in outcrop exposures, striking north-northwest and dipping to the southwest.
Dikes and quartz veins cut the lower Caballape Formation. The strata and intrusive rocks are cut by N30°W striking mafic dikes emplaced at regular intervals (200 m to 600 m), some of which have displacement in the order of tens of metres. These dikes are thought to be related to the Mesozoic diabase intrusions present throughout the district. The most common are sets of thick, boudinaged, and en echelon vein structures that follow foliation/bedding orientation. They are thought to relate in part to movement of quartz during metamorphism. Other quartz veins exist in various orientations that cannot be definitively linked to the structural elements described above.
One of the largest and best-defined stock reaches surface, in the saprolite, in a northeast-trending zone in the Potaso area on the south edge of the Cristinas deposit. The diorite, located north of the Potaso area, is asymmetric in a north-south section: it has a sub-vertical northwest face while its roof is shallowly inclined, dipping south at an angle of approximately 30° beneath the northern edge of the Brisas de Cuyuni deposit. This diorite stock occupies the gap in economic mineralization between the Cristinas and Brisas de Cuyuni deposits. The second diorite stock is located in the northern part of the Cristinas concessions, where it occupies the gap in mineralization between the Mesones and Morrocoy areas.
BRISAS
A possible deposit analogy is of a copper porphyry forming over a magmatic source (yet to be discovered) that was very rich in boron. A peraluminous granite might fit the boron requirements and a sufficient volume of basaltic/andesitic rock could provide the copper. Thin lenses of high Cu and Mo extending away along bedding/foliation planes could be the result of periodic high confining pressures within the Blue Whale that forced mineralizing fluids outward along these planes.
There are four distinct types of gold and copper mineralization present at Brisas, defined by geometry, associated minerals, and the gold-copper ratio. These zones are the Blue Whale body, disseminated gold + pyrite ± copper, disseminated high copper, and shear-hosted gold. Only the first three types are encountered within the proposed pit geometry.
The Blue Whale mineralized body is a discrete, sharply bounded, flattened, cigar-shaped feature that trends more or less parallel to the local schistosity and plunges approximately 35° southwest.
Mineralogically, the Blue Whale is a sericite-tourmaline-pyrite-chalcopyrite-quartz schist, with a smaller volume of quartz-tourmaline-sulphide breccia.
The bulk of mineralization occurs in disseminated, coalescing, lensoid bodies, and high in gold and in most cases low in copper. These bodies lie almost exclusively in the lapilli-rich, rapidly alternating sequence of tuffaceous units and are clearly aligned along foliation. Together, these lenses form a generally well defined mineralized band, which mimics the dip of the foliation/bedding and remains open at depth. It remains at a similar thickness from the northern concession boundary for a distance of 1.4 km south, after which, it tapers rapidly. Alteration minerals characteristic of these lenses are epidote, chlorite, secondary biotite, and sericite.
The gold in the stratiform lenses is highly disseminated but only roughly associated with high occurrences of pyrite. Fine-scale sub-sampling of three metre assay intervals indicates good correlation between gold and small (<1 cm) calcite/quartz veins. Correlation also exists with zones of high occurrence of epidote, and in lapilli-sized lithic fragments that have been partially to completely replaced by epidote and sulphides. Sub-sampling evidence also suggests that gold is more evenly distributed through the rock near the center of the large mineralized lenses than it is near the margins. In section, east-west contours of gold grades at 0.75 g/t or 1.0 g/t show a geometry that essentially mimics contours drawn at 0.40 g/t.
Stratiform lenses of high copper with or without high gold underlie the gold+pyrite lenses described above. These lenses outcrop in the northern part of the deposit, and plunge to the south in a manner similar to the Blue Whale and high gold/low copper lenses but with variable dips.
Shear-hosted gold occurrences exist in the southern part of the concession, running parallel to the foliation as with mineralization further north. Stratigraphically, they occur above the large disseminated lenses previously described. The gold and copper grades are erratic and discontinuous.
CRISTINAS
In terms of classification, Cristinas has been assigned to shear zone-hosted systems by some geologists, and to a porphyry association by others; however, several key elements of the Cristinas deposit must be satisfied in any attempt to classify the deposit. The main two styles of mineralization present at Cristinas are:
1. Stratiform mineralization at Conductora, Morrocoy, and Cordova.
2. Hydrothermal breccia-hosted mineralization at Mesones-Sofia.
The Conductora (including Cuatro Muertos and Potaso), Morrocoy, and Cordova areas contain over 95% of the gold resource at Cristinas. Mineralization in these zones (here called Conductora-style mineralization) is stratiform in nature and is concentrated in volcaniclastic units within the mafic-to intermediate-composition volcaniclastic host sequence.
Mineralization occurs in a greater than three-kilometre long, north-trending zone that dips moderately (30° to 40°) to the west, sub-parallel to the volcanic stratigraphy and to the pervasive (S1) cleavage. Gold mineralization is associated with a sulphide assemblage that consists essentially of pyrite and chalcopyrite.
Quartz-sulphide veins are rare, but where they do occur, they are in zones of intense secondary biotite development against which they have indistinct margins and are associated with multi-ounce gold values. Higher than average gold grades (>2 g/t) are associated with areas in which pyrite occurs as coarse clots up to 2 cm in diameter in zones of intense secondary biotite alteration. Generally, however, the sulphides are fine-grained, and much more so than in Mesones-Sofia.
Mineralization in Mesones-Sofia is concentrated in the quartz-tourmaline-sulphide-calcite vein breccias and extends laterally into the adjacent country rocks. The breccias are sufficiently closely spaced that the country rock between them also constitutes ore in the central part of Mesones-Sofia. Grades in the country rock on the periphery of the system decrease as the distance between the breccias increase.