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Maps & Photos
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Leach Pads |
Processing Facility |
Processing Facility |
Quartz Veinlets |
Quartz Veinlets |
Rock Sample |
Creston Pit |
Grand Central Pit |
Pit |
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Project Description
The past producing La Colorada gold-silver mine property is located approximately 40 km southeast of Hermosillo, Sonora State, Mexico. La Colorada originally operated as a high-grade underground mine, which closed at the start of the Mexican Revolution in 1914. During the period 1993-2000 Eldorado Gold Corp developed a bulk tonnage heap leach operation from several open pits; although the operation was sold in late 2000, production continued by a private Mexican owner until April 2002. La Colorada was until recently Sonora's largest historic gold producer. Currently the La Herradura mine is Sonora's largest producing gold mine.
During the main historic mining period from 1876-1914 the production of more than 3 million ounces of gold was recorded. In I990 the Mexican Geological Service (SGM) measured 1.5 million tons of tailings that were utilized at the start of the open pit production by Eldorado in 1993. The last formal resource estimates for the open pit project were done by Eldorado in 2000. Eldorado published estimated bulk tonnage open pit reserves of 4,115,200 tonnes averaging 1.18 g/t gold (155,900 ounces) within an open pit resources of 21,534,300 tonnes at 0.87 g/t gold (599,300 ounces, total). Production records provided by the current owner show 3,617,340 tonnes of about 0.9 g/t gold were mined following that estimate. In early 1998 Eldorado reported an intersection of 9.4 metres of 31.27 g/t gold which included 3 metres of 80.14 g/t gold. (These estimates are not compliant with NI 43-101 and should not be relied upon, and are reproduced as historic reporting only. Pediment has not independently verified these estimates.)
Geological Background
The La Colorada gold vein deposits are hosted in a volcano-sedimentary sequence that has been locally altered to skarn by magma intrusions. Veins are focused along east-west and northeast-southwest trending structures that dip to the north and northwest at moderate angles, and cut across the skarn and intrusions. Surface mining was focused along three structures, the upper parts of which flare out into stockwork zones. Eight different structures in the La Colorada mine area appear to have older underground workings in gold bearing quartz veins. Past reports indicated the gold deposits formed under mesothermal or deep epithermal conditions, and implied a genetic relationship to the Cretaceous aged magma intrusions that created the skarn. Recent fluid-inclusion studies on veins indicate a low-temperature regime in the epithermal range, and radiometric age determinations indicate ages younger then those for the Cretaceous period of magma intrusion. In addition to this, recent investigations indicate some veins cut Miocene aged volcanic rocks, which suggests the vein forming period at La Colorada is as young as the veins of the Sierra Madre Occidental gold-silver belt located to the east of La Colorada.
Current Exploration
Pediment plans initially to conduct studies of the engineering and environmental parameters for dealing with the existing resource and workings while it completes database and geological studies to outline new targets for testing as possible high-grade ore sources. Pediment's primary goal is to test the project's high-grade vein potential, using exploration parameters for epithermal gold-silver systems. This will include evaluating both the bulk tonnage and high-grade potential of structures for which there is limited indication of past exploration testing.
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