Interest in the Tucker Hill area goes back to 1949 when a group of local prospectors staked claims on outcropping perlite located in the northwestern portion of the present property block. A bulk sample expansion test was favorable, and small-scale mining was conducted until 1954. Mining was concentrated on an area that was easily accessible but contained a high percentage of obsidian nodules. Adjacent areas of high-purity perlite went unrecognized.

In the early 1980's, geologists conducting reconnaissance in the area identified high-quality perlite south of the old mine. After continued evaluation through core drilling and bulk sampling the presence of a significant resource of commercial grade perlite was confirmed. The evaluation of the property continued though to the mid 1990's at which time a decision was made to move forward with development. Cornerstone a public company was formed and construction of the processing plant began in 1996, with production commencing in February of 1997.

Seven Peaks Mining Co. purchased the operation in early 1999. After acquiring the operation, Seven Peaks Mining Inc. embarked on a $1.5 million dollar program to renovate and expand the processing plant.

Local Geology

The Tucker Hill rhyolite dome complex is a package of cooling units related to several rhyolitic vents that originated from a single volcanic event. As a result of differential cooling, Tucker Hill demonstrates distinct lateral and vertical zonation (see geologic cross section). Two major cooling units are recognized, an outer chill margin and an inner rhyolitic core. Vesicle (air pocket) abundance within the rock increases outwards from the rhyolite core through the chill margin as a result of degassing and quenching of the once molten lava.

The chill margin was originally obsidian that was converted to perlite as the result of secondary hydration through continued contact with meteoric waters. The obsidian that remains is found as local zones of "apache tiers".

The chill margin contains various sub-units of perlite ore. The perlite sub-units are based on textural differences that resulted from variable degassing. The textures have been extensively mapped at the Tucker Hill pit in order to maintain a high quality product.

Differential erosion of the Tucker Hill lava dome has removed portions of the outer glass envelope, exposing the rhyolite core. (see geologic cross section)