SANTA MARIE DEL ORO PROPERTY GROUND MAGNETIC SURVEY

REVIEW

RTP Magnetics Looking Southeast

James L. Wright M.Sc. March 26, 2012

This review concerns a ground magnetic survey completed over the Santa Marie del Oro property. Figure 1 presents the reduced to pole (RTP) 50m upward continued (UC) magnetic image overlain by an interpretation. Structures are denoted with dashed lines of two weights to indicate magnitude, contacts have dotted lines and intrusions are hatched polygons.

FIGURE 1: RTP UC 50m Ground Magnetics overlain by Interpretation

Two major structures or lineaments traverse the survey in a north-northwest trend. Cutting these structures and the lithologic package are a profusion of north-south to slightly east of north structures. These structures traverse the entire area covered by the survey, but are undetectable in areas with low magnetic relief, such as the Tsi unit. The structures definitely cut and offset Lineament 1 but not Lineament 2, suggesting the last movement on Lineament 2 post-dates development of the north-south structures. Alternatively, Lineament 2 could mark the boundary of young basin fill material lapping on to old rocks. Offsets along Lineament 1 exhibit both right and left lateral apparent movement. Such geometry would be consistent with predominantly dip slip movement on the north-south set coupled with a shallow dip of the magnetic units east of Lineament 1. The Tan and Tvr units east of the Lineament’s northern extent dip to the west at approximately 45°, which would not explain the apparent lateral offsets or abrupt termination of the high magnetic values associated with the Tan and Tvr. The west flanking magnetic low along the northern portion of Lineament 1 is indicative of a magnetic body dipping to the east. Further south the low diminishes and the lineament is defined as a simple change in the magnitude and texture of the magnetics. In summary,

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Lineament 1 is interpreted as a structure which places Tan and Tvr against Tsi. The southern portion of the structure appears to be high angle, which rotates to an easterly dipping structure along the northern portion.

FIGURE 2: Model Profiles over RTP Magnetics

Figure 2 shows two model profiles over the RTP magnetic image. Profile 1 (PROF1) traverses the northern portion of Lineament 1 and is intended to investigate the geometry along this portion. Results of the model are presented in Figure 3 (Vertical Exaggeration: 3). The green dashed line is the observed data and the solid black line the model response. An approximate fit to the data is noted. A body dipping approximately 10° to the east with a maximum thickness of 100m and width of 1500m is indicated. Depth to the shallow western edge is approximately 50m. The sharp western end is responsible for the prominent west flanking magnetic low. A magnetic susceptibility of 15000 x 106 cgs is very high and typical for mafic to ultramafic rocks or skarn. The model geometry does not fit a westerly dipping package of volcanic rocks with intermediate composition. However, the sharp western edge would be consistent with structural faceting by a shallow east dipping Lineament 1. The north-south structures further confound the interpretation. One possible explanation would be skarn development at the base of the Tertiary rocks within carbonate units of the underlying Jurassic complex and/or within the basal Tertiary (Tcg) unit.

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FIGURE 3: PROF1 Magnetic Model Looking North (VE = ~3)

FIGURE 4: PROF2 Magnetic Model Looking Northeast (VE ~0)

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Profile 2 (PROF2) investigates the interpreted intrusion beneath the Tsi gravels and sandstones. Results of the model are presented in Figure 3 (Vertical Exaggeration: 0) with a reasonable fit noted. The geometry is best described as a steep sided vertical cylinder with depth to top of approximately 125m and radius of approximately 1000m. A magnetic susceptibility of 3000 x 106 cgs is typical of mafic intrusive rocks. The intrusion, like all rocks in the survey, appears to be cut by several north-south structures. Most significant amongst these is a large north-south structure which dissects the intrusion into two portions (see Figure 1).

FIGURE 5: Magnetics, Structures and Veins

Figure 5 shows the geology over magnetics with veins as red lines. Also shown are the interpreted structures. All the veins fall northeast of Lineament 1 in the area traversed by the swarm of north-south structures. Close examination of the veins reveals terminations, offsets and even deflections along the north-south structures. This suggests the north-south structures may have been active during the time of vein development and could host veins. Of particular note is the set of large structures extend south to cut the intrusion. The northern extensions seem to control veins within the Tgr. Lineament 1 along the northern portion is interpreted to dip to the east as do the know veins further east. Geometry of the magnetic anomalies along this portion of the lineament doesn’t match well with the mapped geology, suggesting alternative sources to the anomalies other than the volcanic rocks. Skarn development near or below the base of the Tertiary section is hypothesized as one such source.

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