San Martin Prospect Report 24Aug05

8/21/2019 San Martin Prospect Report 24Aug05

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Field report on San Martin prospect, southern PerúEric Nelson and Andreas Dietrich

20 June 2005

The San Martin prospect was visited by Eric Nelson and Andreas Dietrich along with

Jorge Chavez on 20 June 2005 for less than 2 hours. The San Martin prospect exposes awide zone of silicified faults and veins with a strike length of ~1.5 km, a width of over300 m, and a high elevation exposure of ~4900 m (Fig. 1). It was reported that there are

many other veins in the district that we did not visit (see Fig. 1). The vein system aligns

with a district-scale lineament what may indicate a well developed structural corridor.

We visited only the central zone of quartz veins in silicified outcrops with some old

Spanish workings. These outcrops are hosted primarily in rhyolitic (?) dome rocks aswell as andesitic volcanic rocks. The veins visited contain grey quartz, local barite,

breccia zones with gray silica matrix (Fig. 2), and numerous small faults mostly parallel

to the veins. The presence of barite may indicate that the exposed veins are at the margin

of the mineralizing system. Anomalies on surface and in 2 of 8 drill holes (25% successrate) were reported to include very high Ag (kilograms) and high Zn-Pb.

The vein system we visited is a very wide zone of silicification, brecciation, and veining,and thus represents a relatively significant structure. Brecciation promotes open space

and is often a good indicator of a robust system. In addition, the vein zone hosted by the

dome projects through a saddle and can be traced as a color anomaly for at least anotherkilometer (Fig. 3), suggesting that the mineralized structure continues to the east an

unknown distance.

It was reported that the area visited is present on the northern, brecciated edge of the

volcanic dome. This geologic setting should be mapped in some detail in order todetermine volcanic facies (and associated relative permeability and alteration) and map

possible ring structures (and their orientation and alteration). Map and describe carefullythe breccias and determine if they are structurally controlled tabular bodies and/or have

pipelike geometries; determine if they formed by volcanic processes or

structural/hydrothermal processes. As seen in the Selene/Explorador district suchvolcanic centers and dome rocks are important sites for volcanic-hosted epithermal ore

deposits typical of the southern Peruvian volcanic arc.

Structural kinematic data collected (slickenlines) show mostly steep rake angles

indicating that the veins formed mostly as normal faults (Fig. 4). Fault plane kinematic

indicators and map patterns of vein also indicate a component of sinistral (?) strike-slipfaulting (Fig. 1).





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Figure 2. Gray silica matrix breccia in San Martin vein system.

Figure 4. Eastern continuation of San Martin “fault zone”, east of silicified vein zone.



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Because of the size of the vein system, andgood anomalies at depth in some of the drill

holes, it is recommended that geological and

alteration mapping continue in the district andthat other drill targets be identified. Map and

describe carefully breccia bodies. Attentioncould be paid to covered areas and lineartopographic features. Contacts between

covered areas and exposed host rock are often

observed to be sharply defined and to coincide

in strike with the general trend. Thus coveredareas may bear additional potential for vein

structures.

The vein system visited is very wide but

individual veins are relatively narrow. The

potential exists for ore shoots in local fault jogs, vein intersections, or possibly at depth

where the vein system may join to form a larger structure. In the latter case one should

observe in drill core a decreasing number of mineralized structures and increasing width

of individual veins with depth. On the contrary if vein (veinlet) density maintainsconstant this may indicate that mineralization was poorly focused and is rather dispersed

with reduced potential for the development of veins wide and rich enough for mining.

Because slickenlines have near 90° rakes (Fig. 4), the ore shoots are predicted to be sub-

horizontal within the veins. However, this is based on limited data, and more slickenlinestudies are recommended throughout the entire San Martin district. If structural openings

were preferentially of horizontal orientation, economic mineralization may be located at acertain elevation and vertically rather than horizontally spaced drilling could help to

explore the potential of these structures.

The amount of drilling and the depth tested may not be adequate to locate individual ore

shoots. If other good drilling results are obtained in the region, it is recommended that

further drilling be designed in the vein system we visited. More slickenline studies arerecommended in order to use the drill-target design procedure shown in Fig. 5 (developed

recently on the Cerro Blanco prospect in Chile). Deeper drilling is also recommended.

The presence of a high block of Grupo Yura basement rock indicates strong blockfaulting, although some of the structural relief could be related to paleo-topography, such

that some of the block faulting occurred prior to deposition of the volcanic rocks

(Tacaza?). The veins observed truncate along strike against the block of Yura Groupbasement exposed at relatively low elevation to the west along the strike valley. Either

post-mineralization cross faulting has displaced the veins up to the west, or the Yura

basement block was uplifted prior to mineralization but failed to become mineralized dueto inherent rheological and/or chemical properties. With the first model, the Yura block

should expose evidence of hydrothermal fluid bypass flow at a deeper level below the

m a in o u tc r o p t r e n d

D

D

U

U

Figure 4. Stereonet showing structural data from

San Martin prospect; great circles represent

fault/veins. Inset shows interpretation with main

vein striking WNW and dipping steeply south and

north, and second-order veins striking ENE.



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(now eroded) mineralized Tertiary volcanic rocks. With the second model, the Yurablock should expose weak mineralization or alteration developed at a level comparable to

mineralized rocks seen along strike in Tertiary volcanic rocks. Also, with this model the

intersection zones of veins and cross faults are exploration targets. These models shouldbe tested with alteration mapping in the Yura and surrounding blocks and by determining

offsets if possible and if the overlying(?) volcanic rocks on the surrounding ridges areoffset.

Figure 5. Procedure for calculating X and Y offset and step-out distances in drill hole design in vein systems with

raking ore shoots whose rake is related to fault/vein slickenlines.

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San Martin Prospect Report 24Aug05