Fig. 16. Surface geological map of the San Juan deposit showing surface rock geochemistry for silver.
|The Cuale VMS District is centered 4 kilometres southwest of the pueblo of Cuale, the center of the Ejido of Cuale. The primary business of the Ejido is lumber harvesting. Cattle ranching and farming are secondary activities. Industrias Peñoles maintains the rights to the 308 Ha "La Prieta" concession. They remain active with care-and-maintenance activities in the District.
The known VMS prospects in the Cuale district occur in an area 4 kilometres long by 2.5 kilometres wide with the long dimension of this area oriented northwest (Fig. 1). The associated geochemical anomaly is somewhat larger, with dimensions of 8 kilometres by 4 kilometres. Most historic mining activity was centered on near-surface VMS deposits in a 200 to 400 meter thick section of the Ore Horizon (Unit 1A) that outcrops between the southeastern flank of Cerro Canton and eastern flank of Cerro Caracol. This group of deposits includes San Nicolas, Refugio, Naricero, Socorredora, Los Chivos, Coloradita and La Prieta. East of the Corazon Canyon, the Ore Horizon is thinner (40 m to 120 m thick), but present and mineralized on both the western and eastern flanks of Cerro Descubriadora where it outcrops below a cap of rhyolite flows on the order of 200 m thick. Several deposits, including Jesus Maria, San Juan, Grandeza, Las Talpas, San Antoñio, Peregrina and San Rafael belong to this second group of deposits. Compared to other VMS Districts in western Jalisco State on Company Property, Cuale is unique in that there is a large, hypabyssal rhyolite flow-dome characterized by spherulites and lithopysae (Unit 10C_FW) that intrudes into and underlies the District. This dome is incised by the Arroyo Corazon over a vertical range of at least 960 m south of the Corazon plant.
Mortensen et al. (2008) analysed lead isotopes from galena in 2 samples from Cuale. They observe that these samples yield radiogenic compositions typical of most other samples from the Guerrero Terrane. At Cuale, the most likely source of radiogenic lead was the pelitic schist in the pre-Jurassic basement as there are no continent-derived sediments interlayered with the Cuale Volcanic Sequence.
JESUS MARIA AND PATROCINIOIn 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 Penoles' topography.
In 2008, the Company drilled 1607 metres between Jesus Maria and Patrocinio in 13 reverse circulation drill holes to confirm and expand upon Zimapan's historic drilling results. Drill holes ZIM16, 19 and 30 have intercepted a mineralized body more than 210 metres long, at least 50 metres wide down-dip, and ranging from 17 to 42 metres thick. This body is defined by mineralized intercepts containing more than 5% combined lead and zinc, as well as significant copper values. Overall, the best result is 5.03% Zn, 1.39% Pb, 0.21% Cu and 14 g/t Ag across 41.82m in Hole ZIM30 (Fig. 2).
In 2011, the Company drilled an additional 5 HQ diamond drill holes in the vicinity of ZIM30. Hole ZIM45, collared 5 m southeast of ZIM30 and drilled northerly (essentially a twin of ZIM30) returned values of 3.1% zinc, 0.54% lead, 0.14% copper, 9 g/t silver and 45 ppb gold across 31 meters. ZIM46, drilled 30 meters west of ZIM45 and oriented northeasterly, returned values of 4.74% zinc, 1.10% lead, 0.21% copper, 13 g/t silver and 91 ppb gold across 31.5 meters.
Geologically, zinc-rich mineralization at Jesus Maria occurs below a phenocryst-poor rhyolite flow-dome (unit 10C_BX) characterized by complex flow banding and chaotic flow-breccias on the order of 150 meters thick (Fig. 3). 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 (Unit 1A). The mineralization consists of honey yellow to red sphalerite with galena, chalcopyrite and minor pyrite. These fine metalliferous sediments grade downwards into about 70 meters of 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 10_FW).
The flow-dome above the zinc-rich massive sulfide horizon also contains sulfide-poor gold and silver rich mineralization. Specifically, Hole ZIM43, collared 45 m northeast of ZIM30, intercepted 6 meters of 36 g/t Ag and 0.78 g/t Au in rhyolite flow breccia cross-cut by calcite veining. Similarly, Hole ZIM44, collared 70 meters north of ZIM30 intercepted 24 meters of 66 g/t silver and 0.38 g/t gold, but without any calcite veins. Neither of these two holes was drilled deep enough to cut through the rhyolite flow dome into the underlying zinc-rich sediments.
GRANDEZAGrandeza mine was the largest of the Minas de Oro with historic production of 756 661 tonnes of ore grading 1.89 g/t Au, 22 g/t Ag, 1.41% Pb, 2.35% Zn and 0.2% Cu (Fig. 5). Grandeza was mined by Industrias Peñoles in the mid-1980's. Collectively, there are about 2850 meters of underground workings on six different levels between 2010 meters elevation and 2090 meters elevation, all within a 110 meter long by 70 meter wide area 1.4 kilometers southeast of the Company's Patrocinio Camp. The underground workings are in poor condition, so no field inspections have been completed at this mine.
Historic reports mention that the ore occurs in seams, pockets and pipes in a shattered quartz porphyry. Ore minerals are mainly pyrite, sphalerite, galena and chalcopyrite with minor bornite, covellite and native gold (Kirwin, 1982). Alteration minerals are mainly sericite, quartz, barite, carbonates, gypsum and kaolinite. Industrias Peñoles modeled Grandeza as a vertical, epigenetic stockwork deposit (perhaps similar to San Juan). However, the author of this Report notes that a major control on the deposit may be the brecciated, glassy, chaotic lower contact of a thick rhyolite flow underlain by the black shales of the Ore Horizon (Fig. 6). Such a contact would be a favourable horizon for VMS-style mineralization, as it is in the better-studied Jesus Maria and Talpas deposits 1.5 km to the northwest and 200 m southeast, respectively.
TALPASLas Talpas, also an underground mine, is accessed from a portal 200 meters southeast of Grandeza (Fig. 7). 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. The Company has taken a few rock chip-channel samples with results as follows:
CALDEROCaldero occurs 140 meters southwest of the Talpas Portal at 2078 m elevation. From underground, the mineralization is accessed from the 1990 meter level of Talpas mine. The tunnel goes 70 meters to the southwest, then follows a mineralized horizon for 100 meters to the southeast. There are 5 draw points for ore along this tunnel. A sample cut across the very end of the stope contains 16.5% Zn, 7.7% Pb, 0.35% Cu, 42.5 g/t Ag and 1.6 g/t Au across 1.45 m (sample 25828). Based on the geological interpretation of Fig. 8, Caldero is probably a minor deposit in the rhyolite flows 20 or so meters above the main Ore Horizon (Unit 1A).
EL ROSARIOEl Rosario is 325 meters south of the Talpas portal, and rock dumps outside the mine adits occur at 1980 m elevation and 1920 m elevation. Samples of the rock dumps contain metal values as follows:
SAN RAFAELSan Rafael was clearly a significant historic prospect based on the size of the rock dumps and the number of underground and open pit workings (Fig. 9). 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 outcrops 60 meters southwest of the building at 1850 meters elevation. Here, there is a small stope that follows a VMS sulfide zone oriented 166º/45º WSW. A (weathered) sample cut across a pillar near the surface yielded results of 367 g/t Ag, 1.24 g/t Au and 0.1% Pb across 1 meter (sample 26272). Below the historic workings, at 1825 meters elevation, Industrias Peñoles built an adit 70 meters long oriented NW that cut through the old stope and exposed the mineralization. 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. Industrias Peñoles drilled two holes through San Rafael (possibly) as shown in Fig. 10.
PEREGRINAThe Peregrina workings occur 300 meters northeast of San Antoñio between 2080 and 2110 meters elevation. Stratigraphically, Perigrina appears to be hosted in sediments that overlie the rhyolite flow, a position similar to that reported for the Desmoronado VMS deposits. 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.
SAN ANTOŅIOThe 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.
NARICERONaricero occurs about 170 metres northeast of San Nicolas. It was the largest past producer of the Cuale District with 782 544 tonnes of 0.34 g/t Au, 157 g/t Ag, 1.05% Pb, 2.85% Zn and 0.06% Cu, mainly from an open cut on the west side of the Arroyo Corazon canyon (Hall and Gomez-Torres, 2000). Prior to being worked by Zimapan, a number of independent operators had mined out selected horizons of the Naricero orebody from several underground room and pillar operations.
At Naricero the Ore Horizon is about 160 m thick, and occurs between a quartz-feldspar porphyritic flow (Unit 10C_BX) in the hanging wall and an intrusive, spherulitic quartz-feldspar porphyritic rhyolite flow-dome in the footwall (Unit 10C_FW). Previously mined ore was contained within two horizons that are separated by a stratigraphic interval of 10 to 30 metres. The lower horizon is the thickest, and more laterally extensive having lateral dimensions of 390 by 195 metres (Hall and Gomez-Torres, 2000).
The Lower Naricero Horizon is partially exposed in the bottom of the open pit. The average result of 25 chip-channel and grab samples from 180 metres of exposed strike length is 280 g/t Ag, 0.33 g/t Au, 7.0% Zn, 3.7% Pb and 0.06%Cu. Primary sulfide minerals are sphalerite, pyrite, galena, chalcopyrite and tetrahedrite. Lesser amounts of tetrahedrite-tennantite, geocronite and proustite-pyrargarite are also present (Hall and Gomez-Torres, 2000). Perpendicular and above this high-grade horizon, a continuous chip-channel sample cut across 19.1 metres of silicified tuff beds exposed in the pit wall yielded an average result of 80.4 g/t Ag, 0.5 g/t Au, 0.02% Cu, 0.5% Pb and 1.4% Zn.
In 2008, the Company drilled two holes into Naricero. Hole ZIM 25, located 70 metres southeast of the open pit, intercepted two zones of silver-rich, but sulfide poor mineralization. Hole ZIM 28, located 100 metres west of the open pit, was intended to explore for the western strike extent of Naricero, but the hole broke into two levels of mined-out underground workings. The upper level occurs between 1884 and 1890 metres elevation, and the lower level occurs between 1845 and 1851 metres elevation. A partial sample of the upper level contains 74 g/t Ag, 3.09% Zn and 0.42% Pb across 2.04 metres.
SAN NICOLASThe San Nicolas deposit is about 1700 metres northwest of San Juan on the west side of the Arroyo Corazon valley. It consists of two adits and several open cuts on a steep south-facing slope. Historic production in the 1980's totaled 79 965 tonnes of 0.19 g/t Au, 121 g/t Ag, 1.57% Pb, 3.18% Zn and 0.136% Cu (Hall and Gomez-Torres, 2000). Mineralization occurs at the contact between the spherulitic rhyolite flow-dome (Unit 10C_FW) and overlying black argillite intercalated with rhyolite tuff (Unit 1A). Historic drill holes imply that the mineralization was about 25 m thick with lateral dimensions of 100 m by about 70 m. The average result of 5 chip-channel samples cut across an outcrop of the ore left in the bottom of the open pit is 310 g/t Ag, 3.5% Zn, 2.5% Pb and 0.3% Cu across 14 metres (samples 19781 to 19785). About 35 metres to the southeast, a silicified, copper rich zone was identified. A chip channel sample from this area yielded results of 4.2% Cu, 1.1% Pb and 93 g/t Ag across 2 m (sample 26016). Hole ZIM24, drilled to test for a copper-rich stockwork zone under the massive sulfide deposit, had negative results.
REFUGIORefugio is located about 550 metres northwest of Naricero. Past production from the Refugio deposit was 34,569 tonnes of 156 g/t Ag, 0.14 g/t Au, 1.95% Zn, 0.89% Pb and 0.1% Cu (Hall and Gomez-Torres, 2000), mainly from a single adit on the road to El Realiz. El Refugio occurs in black argillite of the Ore Horizon (Unit 1A) below a porphyritic rhyolite flow (Unit 10C_BX). One of the best historic drill hole results from El Refugio was 158 g/t Ag, 0.1 g/t Au, 3.1% Zn, 0.6% Pb and 0.1% Cu across 4.8 m from Hole 205u-Re.
SAN JUANSan Juan is approximately 2 km south-southeast of the Cuale mill. Geologically, it is hosted in porphyritic rhyolite (Unit 10C_INT) that intrudes devitrified rhyolite (Unit 10C_FW) and overlying lapilli tuffs (Unit 10C_FX). This is stratigraphically lower, and probably geologically younger, than most deposits in the Cuale District. Mineralization mainly occurs as dense stockworks in the porphyritic rhyolite, but some minor zones of massive sulfide occur in the sediments marginal to Unit 10C_INT.
In 1985, Compañia Fresñillo completed underground mapping and sampling of several small 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. 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. 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. Overall, the drilling results confirm the following:
REFERENCESHall, 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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