Minera Camargo S.A. de C.V.
Projects
Projects
Minera Camargo is actively exploring the Mexican Ignimbrite Belt for precious metal deposits with partners RNC Gold Inc, Northwestern Mineral Ventures Inc. and Oro Gold Resources Ltd.
In southwestern Mexico, we are exploring exposed windows of the older Guerrero Terrane for precious-metal enriched volcanogenic massive sulfide deposits with International Croesus Ventures Corp.
Metallogeny of the Mexican Ignimbrite Belt
The Mexican Ignimbrite Belt is one of the largest known silicic volcanic fields in the world, and hosts numerous precious metal deposits, including Rosario, Tayoltita, El Sauzal and Tejamen. In 1979, the U.S. Geological Survey informally divided the geology of the Sierra Madre Occidental into a "lower volcanic complex" and "upper volcanic supergroup" (McDowell Clabaugh, S.E., 1979). They reported that: (i) the lower volcanic complex consists of batholithic intrusives and associated extrusive rocks whose ages range from about 100 to 45 Ma (Late Cretaceous to Middle Eocene), and (ii) most [epithermal] mineral deposits occur in the lower volcanic complex. It is unconformably overlain by the upper volcanic supergroup, which: (i) consists of rhyolite and rhyodacitic ignimbrites with minor mafic flows towards the top of the sequence whose ages range between 34 and 27 Ma, and (ii) contain relatively few [epithermal] mineral deposits compared to the lower volcanic complex.
These generalized definitions and assumptions pervade both historic and recent literature on the Mexican Ignimbrite Belt, mainly because of a lack of detailed mapping in the rugged cliff-country of the Barrancas, where the best exposures of the geology are available. For example, recent work both in the Tayoltita camp and the Espinazo del Diablo (Picachos project area) shows that the "upper volcanic supergroup" is actually composed of three groups: (I) lower composite late Eocene caldera complexes, (II) a sequence of fluvatile sandstones and conglomerates that represents an erosional unconformity, and (III) an upper sequence of Late Oligocene to Early Miocene ignimbrites, flows and domes with minor mafic rocks. (Horner, 1998; Enriquez and Rivera, 1998; and Enriquez and Rivera 1997).
Between the Espinazo del Diablo and Tayoltita, Group I rock units include: (i) a basal section of rhyodacitic ignimbrites up to 1000 m thick (caldera-fill tuffs), (ii) small to regional-scale flow-dome complexes that typically intrude the tuffs, and (iii) about 1000 m of andesitic tuffs, flows and breccias. These rocks represent the remnants of eroded Late Eocene calderas that developed in response to ENE-directed subduction of the Farallon plate below continental Mexico during the latest stages of the Laramide Orogeny (Horner, 1998). Within the volcano-plutonic centers, fracture generation related to tectonic stresses was coincident with circulation of metalliferous hydrothermal fluids, resulting in a major mineralizing event throughout the Western Sierra Madre characterized by the deposition of silver and base-metal rich intermediate sulfidation epithermal veins and disseminations (e.g. Tayoltita, Picachos).
Group II sandstones and conglomerates contain pebbles and grains of rhyolite, andesite, diorite, quartz monzonite and mineralized quartz. They represent a period of erosion that lasted up to 10 million years.
Group III ignimbrite sequences and rhyolite flow-dome complexes were generated during a second pulse of magmatic activity related to extension starting in the Oligocene. Buoyant granitic batholiths rising through the mantle generated felsic melts which erupted violently and created younger calderas overlapping and to the west of the older Eocene arc. The felsic ejecta blanketed an area over 1200 km long and up to 300 km wide, thus forming one of the largest continuous ignimbrite expanses in the world. These ignimbrites filled in pre-existing topography between the older Eocene calderas, and buried and preserved many of the older epithermal mineral deposits. At the same time, felsic-flow dome complexes and associated (younger) epithermal deposits were being generated in the caldera collapse structures. Many of the deposits in Oligocene to Miocene rocks near Rosario have characteristics typical of high sulfidation copper-gold deposits.
Picachos
The Picachos project is located in the Espinazo del Diablo caldera 100 km west of Durango City and 40 km SE of Tayoltita. Within the volcanic structure, there are several zones of epithermal precious metal mineralization. The most significant historic workings include intermediate-sulfidation epithermal Ag-Au (Pb, Zn, Cu) prospects El Toro, Los Angeles and Los Cochis. Guadalupe and El Pino are lower sulfidation Ag-Au deposits with almost no base metal values.
El Toro
El Toro is located in the central part of a large sericitic alteration zone hosted in rhyodacitic caldera-fill lapilli tuffs. Alteration and mineralization associated with the El Toro hydrothermal system has been traced intermittently on surface for about 650 m over a width of about 200 m, and is thought to extend as least as far as the ridge east of San Cristóbal for a total of 1300 m along strike to the WSW. Within this area, there are 23 samples with average silver and gold values of 494 g/t and 1.08 g/t, respectively. The maximum values are 2980 g/t Ag and 6.81 g/t Au. A single sample from a quartz-rich gossan east of San Cristóbal contains 2.1 g/t Au and 5.2 g/t Ag, and is thought to represent the surface expression of the El Toro vein in this area. The vein occurs in pervasively silicified and sericitized feldspar-phyric felsic tuff with pyrite disseminations. Mineralization is closely associated quartz-calcite-piedmontite (Mn epidote) - sulfide/sulfosalt veins, stringers and breccias within the alteration zone. Ore minerals include pyrite, galena, sphalerite, chalcopyrite, enargite and acanthite. The vein is difficult to sample systematically in the stope, but appears to contain about 537 g/t Ag and 1.6 g/t Au across at least 4.2 m.
Los Angeles
Several historic workings are centered on the Los Angeles veins over an area 1.6 km long and up to 300 m wide. There are two open stopes, La Planilla and Las Palomas, as well as several exploration adits and tunnels. The largest of these are Los Murciélagos, La Chinakatera and El Carrizal. The average metal content of 70 samples taken from these workings is 0.76g/t Au and 118.3 g/t Ag. Maximum values are 2782 g/t Ag and 17.44 g/t Au. The best gold grades come a 10 meter wide mineralized zone intersected in the Chinakatera exploration adit 60 m from the entrance. The zone trends 250º and dips steeply NW. Six chip-channel samples yield an average grade of 90 g/t Ag, 3.1 g/t Au, 0.3% Pb and 0.3% Zn across the entire 10 m width. This includes a 1.4 m wide zone that contains 262 g/t Ag, 17.45 g/t Au and 0.8% Pb+Zn (sample 4429). Mineralization consists of sub parallel veins and stringers of coarse-grained quartz, calcite, pyrite, sphalerite, galena and chalcopyrite in a matrix of silicified, sericite-altered felsic tuff. Acanthite is probably the main silver-bearing mineral, but it was not positively identified in thin section or with the SEM. The best silver grade is a grab sample of ore material from the Las Palomas open stope (pictured on front cover). There is almost no vein material left in this stope that is accessible for sampling, so this working is not well evaluated. Close to Las Palomas, a test pit sunk on Veta de La Luz returned values of 0.6 g/t Au and 536 g/t Ag across 0.4 m. More importantly, the alteration assemblage includes clinozoisite (colourless epidote), suggesting that the hydrothermal system was hotter to the southwest.
Los Cochis
Most of the historic workings in the Los Cochis area occur on an ENE structural trend centered on Veta Las Chivas between the La Tolva adit and the Don Andres showing area in the arroyo Los Cochis over a strikelength of 900 m. The zone is unexplored (open) to the west. The eastern part of the Las Chivas Vein appears to be offset along a northwest trending strike-slip fault that outcrops in the arroyo Los Cochis. It is quite likely that the Los Cochis Mine, (reportedly a Spanish mine that has now been buried by a landslide), exploited the offset portion of this vein. Average metal values for all 57 rock samples taken from the Las Chivas mineralized trend area are 403 g/t Ag, 956 ppm Cu, 1.5% Pb and 6.2% Zn. If only the channel samples across La Tolva, Campamento, the fourth cross-cut in Las Chivas and the Don Andres showing are considered, they yield an average grade of 0.9g/t Au, 297 g/t Ag, 935 ppm Cu, 1.3% Pb and 6.2% Zn across an average width of 2.7 m.
Centered roughly 100 m south of the La Chivas Vein, the sub parallel "El Fresno" mineralized trend is defined by an ENE trending series of rock dumps, patchy bedrock exposures and mostly caved old workings. The average metal values for 35 rock samples from this zone are 647 g/t Ag, 893 ppm Cu, 2% Zn and 1.8% Pb. Surprisingly, the best results come from chip and channel samples of disseminated mineralization with no apparent veins or stringers. For example, a sample across the east wall of Mina El Fresno yielded 1275 g/t Ag, 0.1%Cu, 0.8% Pb and 0.7% Zn across 2.5 m. The El Fresno trend is not as well mapped as the Las Chivas trend (due to a lack of exposure) but the soil geochemistry suggests that the zone is continuous over a strikelength of at least 1.1 km, and is still open to the west.
El Pino-Guadalupe
The El Pino vein-breccia is hosted in andesite, and has been traced intermittently on surface with 36 samples between 1400 and 1640 m elevation over a strikelength of 600 m to the NNW. The samples average 1.75 g/t Au and 259.2 g/t Ag, with maximum values of 11.12 g/t Au and 810 g/t Ag. There are at least two main subparallel breccia zones, and numerous colloform veins with gold and silver values in the alteration zone between the main breccias. The most significant, the Breccia Madre, is best exposed in the Upper Stope where an average grade of 462 g/t Ag and 2.6 g/t Au across a true width of 5.2 m was obtained. The core of the mineralized zone is characterized by pervasive potassic alteration and quartz veining. Ore minerals include pyrite, hematite, electrum, acanthite and rare sphalerite and galena. Distal to mineralization, the alteration grades from quartz-epidote dominant propylite to chlorite-calcite dominant propylite. El Pino appears to be part of a larger NNW trending fault zone related to the emplacement of a large diorite dike at least 600 m wide and 6 km long.
The Minas Guadalupe are characterized by similar alteration patterns to those found at El Pino, and the mineralization is essentially identical. Four samples taken 160 m apart from the North and South workings average 8.27 g/t Au and 986.5 g/t Ag. The maximum values were 28.85 g/t Au and 2627.6 g/t Ag. Both of these values are from a 0.25 m wide chip-channel sample across a NW trending vein exposed in a 3 m long adit.
View the Picachos PDF document here. This presentation is also available as a PowerPoint Slide Presentation - although it is a 20 MByte file best downloaded over a high speed connection. (Slide Viewer)
Tango Gold Project
The Tango concession is located about 25 km NE of Rosario, Sinaloa (Fig. 1), and is located within the Rosario Mining District, one of several significant Au-Ag camps in the Mexican Ignimbrite Belt.
High-sulfidation epithermal gold mineralization on the Tango Property is closely related to the evolution of a Oligocene to Miocene caldera complex that is dominated by rhyolite breccia, welded tuffs and rhyolite flow-dome complexes. The ignimbrites are locally intercalated with aphyric, amydaloidal mafic rocks.
There are several alteration styles observed on the property, but the most important are advanced argillic assemblages as these are associated with gold and base metals. On the Tango concession, this assemblage includes pyrophyllite, quartz, epidote, muscovite, kaolinite and alunite. ASTER alteration mapping suggests that alunite might be more abundant than kaolinite. The advanced argillic alteration assemblage is characteristic of the high-sulfidation epithermal environment.
Values for gold, copper, arsenic, lead, zinc, vanadium and manganese are markedly anomalous in soil samples from a 1 km * 2 km grid. Gold concentrations are most remarkable, with fully half of the samples containing more than 15 ppb Au, and 5% of samples containing more than 763 ppb Au. The boundary between strongly anomalous gold in soil and moderately anomalous values approximates the contact between rhyolite and the older andesites, suggesting that gold was both disseminated throughout the (relatively permeable) ignimbrite pile, and deposited in structures, but only structurally controlled in the older andesites. The multi-element geochemical anomaly is more than 1.5 km long and 1 km wide, and remains open in all directions.
Mina La Gloria was one of the more significant past producers on the Tango concession, and limited sample data from this largely inaccessible stope indicate an average grade of 9.4 g/t Au across 0.8 m. The best sample was from the NW end of the stope, where a result of 21.1 g/t Au and 6 g/t Ag across 0.8m was obtained. The ore contains high values of copper and arsenic, suggesting that primary sulfide mineralization included enargite, a characteristic mineral of high-sulfidation epithermal gold deposits. The highest grades on the property come from the NNW trending Carmen I and II structures. On the Carmen I vein, values of 54 g/t Au and 134 g/t Ag were obtained from quartz-specularite mineralization across 0.4 m.
View Tango Gold Project slide show in PDF file format here. This presentation is also available as a Slide Presentation - although it is a 20 MByte file best downloaded over a high speed connection. (Slide Viewer)
Metallogeny of the Guerrero Terrane
The Guerrero Terrane is a complex island-arc assemblage that was accreted to the Western margin of continental Mexico between the early Cretaceous and the Tertiary. Parts of the Guerrero Terrane are built on schists derived from continental sources, whereas other parts are characterized by oceanic basement assemblages. Exposure of the Guerrero Terrane is limited to isolated windows, usually exposed by uplift above major Cretaceous and younger batholiths.
Jalisco VMS Project
The Jalisco VMS project targets a black shale basin with several volcanogenic massive sulfide deposits hosted in Jurassic submarine volcano-sedimentary rocks built on a basement of pre-Triassic (?) schist. There are three claim blocks with a total surface area of more than 22 000 Ha. These overlap parts of the Cuale, Bramador and Talpa de Allende VMS camps.
View the PDF slide presentation here, or download the PowerPoint presentation (this is a 20 MByte file best downloaded over a high speed connection).
Slide Viewer
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Updated March 13, 2005
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Copyright © 2004 Minera Camargo
Updated January 5, 2005