Tango Porphyry Copper-Gold and Epithermal Gold Project: Rosario, Sinaloa
Summary
The 17,457 Ha Tango Property is centered in Southern Sinaloa State, Mexico, in the municipality of Rosario near geographic co-ordinates 105º45’W and 23º12’ N (1:50 000 mapsheet F13A47). The Property was acquired by staking in early 2003, at the bottom of a prolonged cycle of depressed metal prices. The Project is located in western foothills of the Sierra Madre Occidental, one of the world’s largest silicic igneous provinces, and overlaps the former “Viva Zapata” Mineral Reserve, a project that was staked and explored by the Consejo de Recursos Minerales (now the Servicio Geologico Mexicano -- SGM) in 1983-1984. Later geochemical work by the Consejo at the turn of the millennium highlighted the District as one of the largest contiguous anomalies for gold and base metals in southern Sinaloa and Northern Nayarit. Minera Camargo has confirmed the scale and amplitude of the SGM anomaly, and completed both soil and rock sample geochemistry in most of the anomalous drainages on the Tango Property. Major conclusions of the work completed to date are:
- The Property is underlain by two volcanic sequences: (i) older mafic rocks of probable Paleocene age intruded by quartz monzonite and monzodiorite porphyries that are unconformably overlain by (ii) rhyolitic ignimbrites and flow-domes of probable Oligocene age.
- Mineralization is hosted in: (i) ENE trending fractures and broad metasomatized zones in the older mafic rocks and co-genetic plutonic complex, and (ii) younger NNW trending fractures that cross-cut Oligocene rhyolites as well as the older mafic rocks.
- The plutonic complex is affected by hydrothermal alteration over a mapped area of 5 kilometers by 3 kilometers, and the alteration assemblages are: (i) SODIC ALTERATION characterized by albitization of feldspar, tourmaline breccia and magnetite-quartz veins with or without chalcopyrite, (ii) POTASSIC ALTERATION marked by quartz-biotite greisen with chalcopyrite, magnetite, bornite and biotization of hornblende, K-feldspar alteration of feldspar and tourmaline breccia, (iii) MUSCOVITE alteration that ranges from quartz veins with molybdenum and muscovite-pyrite envelopes to pervasive, coarsely crystalline muscovite greisen, and (iv) PROPYLITIC alteration that occurs peripheral to potassic alteration zones, and can overprint earlier alteration styles. The alteration is typical of PORPHYRY COPPER-GOLD systems. The trimmed average XRAY assay result of 460 rock samples from the Porphyry system is 2040 ppm Cu. Of these samples, 46 contain more than 40 ppm Ag. These silver rich samples zone to the northern fringe of the copper-dominant area and are coincident with peripheral SERICITE alteration.
- High-grade, epithermal gold veins occur in both ENE and WNW trending fractures, mostly in the volcanic rocks above the porphyry. The trimmed average of 1050 fire assays from different Vein prospects on the Property is 1.2 g/t Au and 10.2 g/t Ag, and the best overall result is 25.5 g/t Au and 4.6 g/t Ag across 2.5 meters from the Mina de Salvador. The largest ENE trending Vein is the Cocolmeca Vein, which has been partially mapped for 6.2 kilometers between the mine workings of San Agustin, Los Yegaros, Guayabo, San Antonio and El Pino. The largest WNW trending Vein is El Placer, which has been partially mapped for 4.3 kilometers between Tatemales and La Chorrera.
History
Over one hundred historic workings occur on the Tango Property. Some of these include larger tunnels and stopes such as La Gloria, Infiernillo, Carmen and Mina de Cobre, as well as several smaller workings and pits. Small tahonas (mule operated rock mills) occur at numerous locations, mainly El Placer, La Cocolmeca, San Agustin and La Chorrera. Perhaps 30 or so individual tahonas (gambusino's rock mills) have been located to date.
In 1983, the Consejo de Recursos Minerales (now the Servicio Geologico Mexicano or SGM) staked the “Viva Zapata” concession over a total surface area of 31,705 Ha on behalf of the Mexican Government. Existing claims internal to “Viva Zapata” included Nuestra Senora de La Candelaria, Los Placeres, La Norteñita, San Antonio, San Agustin, La Chorrera, El Rodeo and La Soriana. The existing Properties overlapped most of the known mine workings, including Tatemales, La Gloria, El Inclán, San Antonio, San Agustin and El Placer. Effectively, the District was tied up between 1980 and 1999 when the Government started to release lands due to non-payment of mining duties during a prolonged period of depressed metal prices.
In the late 1990's, a group of Americans drove a tunnel underneath the old workings in the San Agustin mine. The old mine had 5 levels over a 60 m vertical interval connected by a vertical shaft from surface. They drove a 200 m long tunnel from surface into the vein underneath these old workings with the intention of putting the mine into production, but ran out of capital. In 1997, they sold the mine to Thunderbird Projects, who agreed to acquire 100% of the shares of Minas Picacho S.A. de C.V. for: (i) the reimbursement of U.S. $560 000 of exploration expenses, (ii) make underlying payments to the vendors of U.S. $1 300 000, and (iii) issue 5,000,000 shares at a deemed value of $0.24 per share . Systematic underground sampling of the San Agustin Mine by Thunderbird Projects suggested the vein has an average grade of 81.22 g/t Au and 73.36 g/t Ag across 1.2m (Thunderbird Projects news release, 18 June 1997).
Between 1995 and 1998, Esperanza del Oro was active on the Profeta Property, a group of 3 claims overlapping the northern half of what is now the “Tango” concession. They completed a preliminary prospecting, soil sampling and hand trenching program in several phases over a 3 year period. Most of the work was done between Mina La Gloria, Mina Tres Hermanos and Cocolmeca Ranch. Esperanza del Oro was funded by MIM of Australia, but accounting problems and poor metal markets resulted in closure of the Project. Work completed in that time included prospecting, soil sampling and some channel sampling across selected outcrops. Fifty percent of the soil samples contained anomalous gold concentrations of 9 ppb or more, with a maximum value of 1509 ppb Au. Silver, As, Bi, Cd, Cu, Pb and Zn values were also markedly anomalous.
In 2000, the SGM completed regional geological mapping and stream sediment geochemical sampling of the El Salto mapsheet. The Tango concessions overlap the best part of a regional scale polymetallic anomaly for gold, copper, lead, zinc and other metals.
Geology
The Tango Property overlaps a complex volcano-plutonic assemblage that consists of: (i) basaltic andesite and basaltic trachyandesite of probable Paleocene age at the base, (ii) bi-modal dacitic flows, volcaniclastics and scoriaceous basalt flows, (iii) a monzonite-monzodiorite plutonic complex, that are unconformably overlain by (iv) rhyolitic tuffs and intrusions of probable Oligocene age. No radiometric age dating has been done on the Property, however, granodiorites located about 50 km to the north of Sitios de Picacho at Malpica were dated at 54.1 +/- 0.3 Ma (Early Eocene; Barra et. al, 2005). The older mafic rocks are mainly exposed at lower elevations between 300 and 800 meters in the arroyos El Placer and La Verdosa. Monzodiorite outcrops mainly north of Sitios de Picacho. Younger rhyolites dominate the heights between 900 and 1200 meters elevation.
Exploration
Regional Stream Sediment Survey
In January of 2006, a detailed stream sediment survey (205 samples) was completed over the entire Property. The survey clearly highlights an area about 6 km long by 4 km wide in the central part of the Property that is co-incident with the known mineral occurrences. The area is defined by about 52 stream sediment samples with concentrations of gold typically higher than 200 ppb, Cu> 69 ppm, Pb> 341 ppm and Zn > 378 ppm. The highest result is 6841 ppb Au from a creek draining the El Placer area.
Summary distribution statistics for 205 stream sediment samples from the Tango Property, Sinaloa, Mexico.
Element (ppm) |
Max. |
Geometric Mean |
Trimmed Mean |
50th |
75th |
90th |
95th |
98th |
Mo |
21.2 |
0.7 |
1.2 |
0.6 |
1.0 |
1.9 |
4.1 |
8.0 |
Cu |
653 |
18 |
39 |
18 |
31 |
69 |
115 |
445 |
Pb |
4298 |
37 |
151 |
20 |
67 |
341 |
658 |
1390 |
Zn |
6773 |
106 |
212 |
74 |
170 |
378 |
653 |
2137 |
Ag |
5.7 |
0.2 |
0.3 |
0.1 |
0.2 |
0.6 |
0.9 |
1.5 |
As |
229 |
11 |
16 |
10 |
17 |
29 |
56 |
82 |
Au_ppb |
6841 |
6 |
248 |
2 |
23 |
525 |
1463 |
5040 |
Sb |
11 |
1 |
2 |
1 |
2 |
3 |
4 |
5 |
V |
880 |
83 |
104 |
83 |
137 |
182 |
222 |
344 |
Soil Geochemical Survey
A total of 1750 B-horizon soil samples were collected from 44 line kilometers of survey grid centered on San Agustin, Cocolmeca and El Placer. Sample spacing was 25 m (slope-corrected) and lines are 100 to 200 m apart. Most overburden on the Property is residual soil from weathering of rock, although in steeper areas some colluvium and talus is present. In general, the overburden is 1-3 meters thick, and characterized by a thin organic layer a few centimeters thick underlain by a brown to red-brown B-horizon soil layer a few 10's of centimeters thick. The soil is underlain by weathered rock. Samples were analyzed for 37 elements by multi-element ICP-MS methods, and metal concentrations for 10 elements are considered markedly anomalous in some samples.
Summary distribution statistics for 1750 B Horizon soil samples from the Tango Property, Sinaloa, Mexico.
| Element (ppm) | Max. |
Geometric Mean |
Trimmed Mean |
50th |
75th |
90th |
95th |
98th |
| Mo | 391 |
0 |
1 |
0 |
1 |
2 |
3 |
6 |
| Cu | 3407 |
26 |
63 |
30 |
69 |
142 |
213 |
435 |
| Pb | >10000 |
68 |
186 |
55 |
140 |
408 |
820 |
1800 |
| Zn | >10000 |
154 |
341 |
126 |
265 |
825 |
1621 |
3056 |
| Ag | >100 |
0.3 |
0.6 |
0.2 |
0.6 |
1.4 |
2.3 |
3.8 |
| As | 2155 |
11 |
15 |
10 |
15 |
27 |
41 |
75 |
| Au_ppb | 24549 |
11 |
115 |
9 |
33 |
180 |
457 |
1782 |
| Sb | 30 |
1 |
1 |
1 |
2 |
2 |
3 |
4 |
| V | 3590 |
55 |
77 |
63 |
101 |
152 |
179 |
223 |
Mineralization
San Agustin, Los Yegaros, La Cocolmeca and El Pino
The San Agustin, Los Yegaros, La Cocolmeca and El Pino are high-grade oreshoots or segments of a major vein located on a deep ENE trending lineament at least 6.2 kilometers long that forms an impressive fault scarp in the center of the Property.
The San Agustin segment outcrops on surface between some prospect pits on the north slope of Cerro San Agustin and the Don Genardo prospect 450 meters to the northeast. On surface, the vein is expressed as a steeply dipping cleavage zone with values of 1.9 g/t Au, 82 g/t Ag, >1% Pb and >1% Zn across 2.5 m (sample 17940; Don Genardo). Samples from underground, however, have markedly higher grades, and muck outside the upper adit by the claim post contains 88.4 g/t Au, 41 g/t Ag, 0.3% Cu, 20% Fe, 2.2% Pb and 2.2% Zn (sample 15927). Mineralization consists of grey quartz with galena, tetrahedrite, pyrite, chalcopyrite, sphalerite and native gold. Several stages of brecciation and silicification are apparent in muck samples, and several contain skeletal quartz (a texture that indicates boiling occurred). About 780 meters NNE of the Don Genardo workings, surface exposures of oxidized quartz veins with values of 114 g/t Ag and 28.6 g/t Au across 0.4 m occur at Los Yegaros, and these veins are thought to represent along-strike continuity of the San Agustin structure.
The Colomeca segment occurs 1300 meters ENE of Los Yegaros, and has been mapped almost continuously for 1650 meters from Guayabo through to San Antonio and Gavilan North. The Cocolmeca Vein consists of gemmy clear quartz with chalcopyrite and chrysocolla and black chlorite in the vein selvedges. The average result of 55 chip-channel samples cut across surface exposures and shallow underground workings on the Cocolmeca Vein is 4.2 g/t Au, 37 g/t Ag, 0.7% Cu, 0.3% Pb and 0.5% Zn across about 1.3 meters. This includes a result of 44.09 g/t Au, 47 g/t Ag, 0.4% Cu, 0.2% Pb, 0.7% Zn and 6.7% Fe across the San Antonio workings (sample 19856), and 347 g/t Ag, 5.2% Cu and 18.6% Fe across 0.7 m across the Guayabo workings (sample 15953).
The El Pino segment occurs about 2400 meters ENE of La Cocolmeca where a sample containing 99 g/t Ag and 22 g/t Au across 0.5 meters (sample 15926) was cut across historic underground workings. No geological mapping has yet been completed on this segment.
El Placer
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