Geochemistry

Results

 - Geochemistry

A picket grid was installed by Teck with sampling stations at 50-meter intervals on north-south trending lines spaced 200-meters apart. Stations were surveyed using a Garmin 12XL GPS unit. Soil samples were obtained by shovelling off an area down to the subcrop and then collecting a sample of “soil” which was then sieved for the fines. The soil grid covers the entire area of the main Rio Grande volcanic center, as well as portions of the smaller center located to the northeast. A total of 1,420 samples were collected and sent to ALS-Chemex in Mendoza for silver and copper analysis by ICP-MS and gold by fire assay with an atomic adsorption (AA) finish. Due to concerns about results and a slow turn-around time, Teck changed to Acme Analytical Labs part way through the program. The samples submitted to Acme were only assayed for copper and gold; although there was a lower detection limit for the gold analyzes.

Copper values in soils (Figures 1 and 2) ranged up to 7,000 ppm, with samples over 200 ppm copper showing a horseshoe-shaped anomaly oriented to the northwest and centered over the central portion of the main volcanic center and its zones of potassic alteration. Other smaller anomalies appear in the south-western part of the grid (e.g., station 612800E, 7230200N), which are due to transported copper minerals (i.e., black copper), or  and to the south of the white knob in line 613400E coincident with the quartz-magnetite stockwork encountered in Trenches # 6 and # 7 (diorite porphyry style mineralization). Several samples form a weak copper anomaly centered on the north-eastern volcanic center.

Gold values in soils (Figures 3 and 4) ranged to a high of 413 ppb, with sample results showing a similar distribution to that of copper; the samples over 20 ppb gold form a horseshoe-shaped body coincident with the copper anomaly. A gold anomaly is also present south of the white knob coincident with the copper anomaly in line 613400E. In the north-eastern volcanic center, samples show a couple of anomalies over 20 ppb and up to 60 ppb. These two anomalies are south of the copper anomaly, and may imply that the copper has been transported and the gold anomaly corresponds to an area of K-feldspar-quartz-magnetite alteration.

Antares Geochemical Sampling

A wide variety of geochemical sample types were collected during Antares’ current Rio Grande exploration campaign:

1. Caminos (515)
2. Trenches (1,284)
3. Outcrop (25)
4. Reverse Circulation Drilling (240)
5. Diamond Drilling (707)
6. TOTAL SAMPLES (2,771)

Results from the surface rock chip and trench sample geochemistry confirm the existence of various Cu-Au mineralized zones arranged in a roughly annular (i.e., circular) pattern about the main Rio Grande alteration area; which were original defined by soil geochemistry (Figures 1 to 4). Additional results from both Teck’s and Antares’ drilling campaigns demonstrate that the best mineralization is structurally controlled within that annular structure, and that strong oxidation of that mineralization can be seen to 200-300 metres depth.

The annular pattern of Cu-Au mineralization is reflected in the soil samples collected by Teck (Figures 1 to 4), surface rock samples (Figures 7 and 18), and trench samples (Figures 5,6 and 19-30). Soil sampling provides an effective, broadly-spaced sampling method for identifying potential zones of mineralization; even in areas of no outcrop. Follow-up surface rock samples and trench samples allow for more detailed definition of the distribution and limits of the mineralization.

The limits of copper oxide mineralization in the Discovery and Sofia zones can be partially constrained on surface by trench samples and at depth by drill-holes RGT_01_01, RGT_01_02 and RGT_01_03. These limits on the distribution of mineralization, both in trenches and drill-holes, indicate that the mineralized zones are controlled by steeply, inward-dipping (i.e., 70°-90°) fault structures and fracture zones, which define the annular ring-like feature.

Using the trench sample results and a 0.1% Cu cut-off grade, it is possible to draw, on surface, a continuous zone of mineralization between the Discovery and Sofia zones (Figure 5). This large zone of mineralization is open to the WSW of the Discovery and NW of the Sofia zones, both areas covered by talus with no outcrop. Using the same 0.1% Cu cut-off grade, several other zones can be identified within the annular pattern; most of these areas have undergone limited trenching and no drilling. Using similar criteria for Au (>0.1 g/t), a similar pattern can be seen (Figure 6).

The annular distribution of Cu-Au and the more structurally-controlled distribution of some Au ±Cu mineralization are visible in the soil, rock chip, and trench data sets. Field relationships suggest that the Cu-Au mineralizing event is early, and overprinted by a pyrite-rich, Au ±Cu mineralizing event. This is shown in trenches T_2, T_4 and T_28, where there is a clear linear structural control, oblique to the annular structure.

In addition to the aforementioned geometric relationships, several geochemical patterns, or associations, can be seen between various elements:

1. Cu-Au-Ag (P-La-Co)
2. P-La-Fe-Ca-V
3. Pb-Zn-Mn-Ag-Au (As-Sb-Cd-B)
4. Cr-Ni-Cu-Co
5. Al-Na-Mg-Ti

Surface Rock Geochemistry

Copper (Cu), Gold (Au) and Silver (Ag)
The copper (Cu) and gold (Au) are distributed in annular, ring-like form (Figures 7 and 9) which mimics the soil anomalies obtained previously by Teck (Figures 1 to 4). In certain areas, Au appears to be controlled ESE-trending structural zones (Figure 8). Field evidence suggests this may be an Au-rich event which overprints the Au associated with the Cu in the annular ring-like feature. Silver (Ag) tends to also form an annular ring-like pattern, accompanying the Cu and Au (Figure 9).

Lead (Pb), Zinc (Zn) and Molybdenum (Mo)
The lead (Pb) and zinc (Zn) are distributed peripheral (i.e., distal) to the annular, ring-like feature (Figures 10 and 11) defined by the Cu and Au (Figures 7 and 8). Strong Pb, and to a lesser extent Zn, anomalies occur to the ENE of the main Rio Grande alteration and mineralization area (Figures 10 and 11). A strong molybdenum (Mo) anomaly is located to the WSW of the principal alteration area (Figure 12); in an area of limited outcrop. 

Arsenic (As), Sulphur (S) and Phosphorous (P)
Arsenic (As) is distributed along the southern margin of the main Rio Grande alteration zone, as well as associated with the alteration zone located to the ENE (Figure 13). There is a suggestion that the elevated arsenic values are controlled by a NW-trending structural corridor (Figure 13).

The distribution of sulphur (S) clearly defines a semi-circular feature located on the north side of the main Rio Grande alteration zone (Figure 14). This most likely corresponds with a pyritic halo, or the partially oxidized remnants of one, or simply the oxidation of sulphides in general. The presence of gypsum / anhydrite may also explain distribution of this anomaly, although no extensive zones of gypsum / anhydrite veining were noted during the surface mapping of this sector.

The distribution of phosphorous (P) (Figure 15) conforms well to the distribution of both Cu and Au (Figures 7 and 8). The phosphorous likely reflects the presence of apatite in the mineralized zones, and therefore may be a good path-finder element for future exploration.

Lanthanum (La), Potassium (K) and Iron (Fe)
Lanthanum (La) is distributed in a similar pattern (Figure 16) to that of P, Cu, Au, and Ag (Figures 15, 7, 8, and 9). Potassium (P) is anomalous in the SW (Figure 17), coincident with the Mo anomaly (Figure 18), and also appears to be associated with the alteration zone located in the ENE. Elevated iron (Fe) appears to occupy areas topographically high and marginal to the main mineralized zones, and to have little correlation with the other elements (Figure 18).

Surface Trench Geochemistry

Copper (Cu), Gold (Au) and Silver (Ag)
The distribution of copper (Cu) and gold (Au) from the trench samples shows in more detail the surface geometry of the mineralization (Figures 19 and 20), compared to that shown by the surface rock samples (Figures 7 and 8). This is especially true in the cases of the Discovery and Sofia zones. The geochemical grids illustrated below for Cu and Au are based on data from both the 2000-2001 Teck trenches and the 2004-2005 Antares trenches; whereas all the other elements are solely based on 2004-2005 Antares data. Teck for unknown reasons elected not to do multi-element analyses on their trench and drill core samples.

The distribution of silver (Ag) is similar to that of Cu and Au, although there are some independent Ag-only anomalies which may represent distinct mineralizing events (Figure 21).

Lead (Pb), Zinc (Zn) and Molybdenum (Mo)
The higher lead (Pb) and zinc (Zn) concentrations are found in T_27 (North Zone) and also in the central part of the Rio Grande alteration system, near trenches T_24 and T_29 (Figures 22 and 23). Higher molybdenum (Mo) values form a crescent-shape in the NE sector (Figure 24). Higher Mo values are also found in the SSE in the vicinity of the Discovery Zone and T_23 (Figure 24). 

Arsenic (As), Sulphur (S) and Phosphorous (P)
Arsenic (As) and sulphur (S) have a similar distribution; occurring in the south (T_23), north (T_27 and T_33), and central (T_24) areas (Figures 25 and 26). Phosphorous (P) correlates well (Figure 27) with the distribution of both Cu and Au (Figures 19 and 20).

Lanthanum (La), Potassium (K) and Iron (Fe)
Lanthanum (La) appears to be associated with phosphorous (P), copper (Cu), and gold (Au) anomalies; however, it also forms an anomaly independent to those elements, in the central part of the Rio Grande system in the vicinity of T_24 and T-29 (Figure 28). Potassium (K) correlates extremely well those areas where strong secondary biotite alteration has been identified; this includes T_26, T-24_central, and T_10_extention (Figure 29). Interestingly, the K does not seem to be strongly reflecting those areas of known K-feldspar alteration. Iron (Fe) appears to be highest in the central portion of the Rio Grande system and also in the parts of the Sofia Zone (Figure 30); where magnetite bearing alteration and breccias have been identified.

Combined Surface Rock and Trench Geochemistry

Copper (Cu) and Gold (Au)
The combined surface rock and trench data for copper (Cu) and gold (Au) are clearly distributed in annular, ring-like feature, however there is also a subtle indication of anomalous values in the centre of that ring structure (Figures 31 and 32). The significance of this is not fully understood, however it could be indicative of the top of a mineralized system.