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Mineralization of the Cuale VMS District


VMS deposits in the Cuale District mainly occur in the Ore Horizon (Unit 1A) between the lower rhyolite flow-dome (Unit 10A) and the upper rhyolite flows (Unit 10U; Fig. 1). San Nicolas, Naricero, Socorredora and San Juan occur near the base of the Ore Horizon, whereas La Coloradita, Jesus Maria-Patrocinio, San Antonio, San Rafael, and Talpas are located near the top contact of the ore horizon with the upper rhyolite. Most historic exploration and mining activity was focused in eroded near-surface exposures of the ore horizon west and north of the Arroyo Corazon (San Nicolas to La Coloradita). However, the author of this report believes the best potential for a new and significant discovery occurs under the capping rhyolites of Unit 10U because (i) it would have formed an aquitard that trapped mineralizing fluids in receptive sediments at the time of ore deposit formation, and (ii) it protected the ore horizon from erosion after the CVS was uplifted from the seafloor onto the continent.


In 1977, Zimapan completed 343 metres of drilling in 12 short, small diameter core holes along the surface outcrop of the Jesus Maria deposit, and 304 metres in 6 holes at Patrocinio. Between 1982 and 1983, Zimapan produced 46,751 tonnes of ore grading 109 g/t Ag, 3.31% Zn, 1.85% Pb, 0.09% Cu and 0.06 g/t Au from the Jesus Maria open pit (Hall and Gomez-Torres, 2000). In 1983 and 1984, an additional 613.2 metres of drilling in 7 exploration holes were completed at Jesus Maria, and 280 metres in 6 more holes were drilled to explore Patrocinio. The historic drilling plan is shown on a topographic map, so it was possible to roughly estimate the locations of the historic drill holes, but differences of more than 50 metres in plan view and 10 metres in elevation exist between the INEGI topography and Zimapan topography.

In 2008, the Company drilled 1607 metres between Jesus Maria and Patrocinio in 13 reverse circulation drill holes to expand upon Zimapan's historic drilling results. The best result was 5.03% Zn, 1.39% Pb, 0.21% Cu and 14 g/t Ag across 41.82m in Hole ZIM30. In 2011, the Company drilled an additional 5 HQ diamond drill holes in the vicinity of ZIM30 to better understand the geological and structural controls of the mineralization. Geologically, the zinc-rich mineralization at Jesus Maria occurs below a phenocryst-poor rhyolite flow-dome (unit 10U) characterized by complex flow banding and chaotic flow-breccias on the order of 300 meters thick. Below the flow-dome, there are about 40 meters of thinly laminated to medium bedded fine tuffs and cherts that host the zinc-rich massive sulfide (Figs. 3 and 4). The mineralization consists of honey yellow to red sphalerite with galena, chalcopyrite and minor pyrite. These fine metalliferous sediments grade downwards into coarse-grained, thickly bedded lapilli tuffs. Below the tuffs, the rock consists of phenocryst poor, devitrified rhyolite domes with abundant lithophysae, spherulites and perlitic fractures (Unit 10A).

A three-point solution of the contact between the upper rhyolite and the zinc-rich sediments in Holes ZIM45, 46 and 47 yields an orientation of 309˚/39˚NE (Fig. 2). This is similar to most surface bedding measurements in the area between La Coloradita and Patrocinio, and confirms the stratigraphic control on the orientation of the mineralization. To capitalize on this knowledge, an exploration drilling program of at least 1725 m in six holes has been laid out down-dip of the known intercepts of ZIM45 and ZIM46. The main target is the zinc-rich contact between the sediments and the capping rhyolite, however, PDH 1 is planned to test the entire width of the sediments under Unit 10U. Information from that hole will be used to adjust the length of the other 5 holes (a contingency of 1000 m is planned for this). If all six holes are successful, a mineralized block on the Jesus Maria horizon will be defined over an area about 100 m wide, 25 m thick (true thickness) and 300 m down-dip. A block of that size with sulfides in it weighs about 3.15 million tonnes, and expected grades are in excess of 5% combined zinc+lead+copper. Potential to discover additional mineralized horizons in the sediments below the target contact is high, and the potential of the Jesus Maria horizon itself is expected to remain open along strike and down-dip towards the village of Cuale.


Las Talpas, an underground mine, is accessed from a portal 200 meters southeast of Grandeza. The Company has mapped seven levels of workings approximately between 1920 and 2020 meters elevation. The mapping shows that collectively, there are more than 3000 meters of underground development at Talpas, all in an area about 200 meters long by 140 meters wide. In the mine, there are several production stopes that are still full of partially broken ore. Zinco has taken a few rock chip-channel samples with results as follows:
The mineralization at Talpas consists of coarsely crystalline dark sphalerite and galena with pyrite, chalcopyrite and minor bornite in markedly silicified, fine-grained, thinly laminated, cherty sedimentary rocks that occur below a thick pile of rhyolite flows. Stratigraphically, this is the same position as Jesus Maria. Bedding appears to be the primary control on mineralization based on visual underground inspections.

Proposed drill hole PDH 7 is positioned on the road 140 m southwest of high-grade sample 25831 (Fig. 5). The hole is designed to test the entire ore horizon between the known mineralization at Talpas, and any potential mineralization between there and the underlying rhyolite lavas of Unit 10A.


San Rafael was clearly a significant historic prospect based on the size of the rock dumps and the number of underground and open pit workings. In the central part of the deposit area, there are the ruins of a stone building 2 meters wide by 3 meters long. The rock dumps are located in a flat area 130 meters long by 180 meters wide immediately north of the building. A sample of massive sphalerite from this main dump contains 621 g/t Ag, 0.14 g/t Au, 8.8% Pb and 20.7% Zn (sample 29976). Several well-built 1 meter wide trails provide access to mine workings surrounding the building, as well as a historic beneficiation plant in the creek about 500 meters below and east of San Rafael. The principal mineralized zone at San Rafael is exposed in an adit 70 meters long oriented NW. Sample 25855, cut across the back, contains 983 g/t Ag, 0.25 g/t Au, 1.6% Zn, 1.2% Pb and 0.5% Cu across 2.5 meters.

The Peregrina workings occur 300 meters northeast of San Antoñio between 2080 and 2110 meters elevation. Stratigraphically, Peregrina appears to be hosted in sediments that overlie the rhyolite flow. Peregrina #1 is an underground tunnel about 50 meters long at 2080 meters elevation, oriented northerly. Sixteen rock-chip channel samples cut by Industrias Peñoles from the rear portion of this adit contain an average value of 85 g/t Ag. Peregrina #2 occurs 125 meters north of Peregrina #1, and is a small room and pillar mine located at 2108 meters elevation. Overall, the workings are 30 meters long to the southeast, and 10 meters wide to the northeast. The average result of 56 underground rock chip-channel samples cut by Industrias Peñoles is 166 g/t Ag and 0.62 g/t Au. The gold-rich nature of the prospect is confirmed by Zinco sample 25888 with 1.1 g/t Au and 56 g/t Ag, taken across 3 meters of mineralized outcrop 18 meters north of the Peregrina #2 adit. Similarly, Zinco sample 25887 returned 0.4 g/t Au and 119 g/t Ag across 1.5 m from surface outcrops exposed south of the Peregrina #2 adit. No historic drill holes occur near the Peregrina workings.

The San Antoñio workings are 900 meters east-southeast of San Juan and occur between 1910 and 1940 meters elevation. The prospects are hosted in fine-grained, silicified rhyolitic tuffs intercalated with chert horizons. San Antoñio #1 is an underground tunnel about 45 meters long at 1928 m elevation, oriented east-southeast. Two chip-channel samples across the back of the adit yield results as follows: (i) 141 g/t Ag across 0.8 meters (sample 25905) and (ii) 359 g/t Ag across 1.5 meters (sample 25906). Detailed geochemical work by Industrias Peñoles shows that the San Antonio #1 adit exposes an 8 meter width of mineralization grading 124 g/t Ag in an ESE trending zone. San Antoñio #2, at 1934 meters elevation, is 60 meters long along an east-southeast trending axis, and at least 15 meters wide to the northeast. Zinco has not done any underground inspections of this mine, but the average geochemical result of 73 underground chip-channel rock samples taken by Industrias Peñoles was 133 g/t Ag. Zinco's own chip-channel sample across the back of the San Antoñio #2 adit near the portal yielded a comparable result of 382 g/t Ag, 0.25 g/t Au, 0.3% Zn and 0.1% Pb across 3 m (sample 25890). Finally, 100 meters northwest of San Antoñio #2, a reconnaissance rock sample from a mineralized outcrop yielded a result of 90 g/t Ag across 0.8 meters (sample 25889). No historic drill holes occur near the San Antoñio prospects.

The area between these known prospects is to be tested by two drill holes as shown in Fig 6. PDH8 has the potential to intercept three mineralized horizons, and PDH9 is designed to test for two, including copper-gold rich (stockwork?) mineralization implied by surface sample 26289 with results of 26 g/t Au, 54 ppm Ag and 1.7% Cu across 4 m.


Modern exploration of San Juan was initiated in 1985, when Compañia Fresñillo completed underground mapping and sampling of several historic prospects and rock dumps located in an area 125 metres long by 100 metres wide. The 1985 map shows the mine grid, but there is no topographic information drawn and it is not possible for the author of this report to reliably geo-reference Fresñillo's map. In the spring of 1986, Fresñillo drilled 530.8 metres of BQ core holes in the northern part of their map area with positive results. Collar locations are not marked in the field. Also in 1986, Compañia Fresñillo completed an IP survey over most of the Cuale District. Thirteen anomalies were identified, including one at San Juan. In the fall of 1986, Hole 555 (located 46 m northwest of ZIM 12) was drilled 153.45 metres deep to test this IP anomaly. Hole 555 intercepted 9.8 m of 35 g/t Ag, 0.4% Zn and 0.1% Pb.

In 2007, Zinco identified one of the strongest geochemical anomalies for silver on its entire VMS Property in the San Juan prospect area. The anomaly is 225 metres long and defined by 19 soil samples in two survey lines 100 metres apart that remains open to the west (an area of steep topography). The average result of these soil samples is 12.4 ppm Ag, 354 ppm Pb, 47 ppb Au, 216 ppm As, 74 ppm Sb and 732 ppm Ba. The highest silver result is 48.9 ppm Ag. The average result of 49 chip channel and grab samples from surface rock samples from this area is 112 g/t Ag, 0.19% Zn, 0.26% Pb, 0.01% Cu and 0.1 g/t Au.

In 2008, the Company drill-tested San Juan and the surrounding area with 2066.52 metres of drilling in 12 reverse-circulation drill holes (Table 11.2). The best overall intercept was 185 g/t Ag, 1.51% Zn and 0.71% Pb across 85.68 m in RC hole ZIM9. HQ diamond drill holes ZIM34 to ZIM 42 were drilled to expand on this intercept. Hole ZIM35, collared 56 meters west of hole ZIM9, returned values of 134 g/t silver, 1.2% zinc, 0.78% lead, 0.01% copper and 63 ppb gold across 63 meters (Fig. 7). Similar results of 136 g/t silver, 0.75% zinc, 0.49% lead, 0.01% copper and 53 ppb gold across 54.65 meters were returned from ZIM39, collared 70 meters northeast of ZIM9. The average result of 15 mineralized intercepts was 81 ppm Ag, 126 ppm Cu, 4515 ppm Pb and 8233 ppm Zn over an average width of 64 meters.

San Juan is located across the valley from Naricero, at the base of the ore horizon sediments (Unit 1A) near the contact with the lavas of the rhyolite flow-dome (Unit 1oA). The mineralization is a precious-metal rich stockwork hosted in porphyritic QFP rhyolite that intrudes both the rhyolite footwall and overlying ore horizon sediments. Sulfides preferentially replace glassy spherulites in the rhyolite, and minor zones of massive sulfide occur in the sediments marginal to the QFP. As the local geological environment of San Juan is considered to be less permissive for development of a large, continuous massive sulfide blanket than the Jesus Maria horizon, no additional drilling is planned there at this time.


Hall, B.V., and Gomez-Torres, P.P., 2000, Geology of the Kuroko-type massive sulfide deposits of the Cuale district, Jalisco state, Mexico: in Sherlock, R. and Logan, M.A.V. eds., VMS Deposits of Latin America: Geological Association of Canada, Mineral Deposits Division Special Publication No. 2, p. 141-161.

Kirwin, D.J., 1982, Investigation report concerning "Kuroko type" massive sulphide mineralization at Cuale, Jalisco, Cia. Fresnillo S.A. de C.V. internal report.

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