Abstract

The Tintic mining district, located roughly 60 miles south of Salt Lake City, is the second most productive district in Utah. The initial discovery in the Tintic district occurred in 1869. With the arrival of the railroad in 1878, the mining operations expanded rapidly making Tintic the most productive district in Utah by 1899. Although district production peaked during the first half of the twentieth century, exploration activities from 1940 to 1970 continued to make significant discoveries under volcanic cover in areas peripheral to the Main Tintic subdistrict. Production declined significantly with the closure of the Burgin mine in 1978, sputtered in the 1990s, and finally came to an end in March 2002 with the closure of the Trixie mine. The district is currently idle except for sporadic exploration activities.

Geologically, the Tintic district is underlain by a thick section of Paleozoic strata that have been strongly folded into north-south trending, asymmetrical anticlines and synclines that have been cut by northeast-trending, right-lateral strike-slip faults. These sedimentary rocks were uplifted, eroded, and covered by early Oligocene calc-alkaline volcanics emanating from a large caldera just to the south of the district. Continuing magmatism resulted in the intrusion of monzonite stocks, plugs, dikes, and sills with associated hydrothermal alteration and mineralization. The area was uplifted on the west during the Basin and Range orogeny, resulting in slight eastward rotation and continuing erosion of the East Tintic Mountains.

The Tintic mining district can be broken down into four subdistricts based on geology, location, and ore occurrence: Main Tintic, East Tintic, Southwest Tintic, and North Tintic. The majority of the production has been derived from sub-vertical copper-gold-silver chimneys and sub-horizontal, carbonate-hosted, lead-zinc-silver ore runs (replacement deposits) of the Main Tintic subdistrict (Morris, 1968). The bulk of the remaining metal production has been derived from the structurally complex ore bodies of the East Tintic subdistrict. The Southwest Tintic subdistrict hosts a large, subeconomic porphyry copper system, which has seen minor production from peripheral high-sulfidation, copper-silver-lead veins. In the North Tintic subdistrict, limited production of zinc-rich replacement ores have been derived from the Scranton and other small mines.

Total district production is nearly 20 million tons, which at current metal prices would translates to well over three billion dollars. Roughly 90 percent of this production has come from irregular, precious metal-rich polymetallic base metal replacement ores. Silver (42 percent at modern metal prices) has been the most valuable product in the district followed by significant gold (29 percent) and lead values (17 percent) with lesser contributions by copper (6 percent) and zinc (6 percent). Not included in these figures, is the production of well over one million tons of halloysite clay, mainly from the Dragon mine.