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Ammolite

Formation, occurrence, and extraction of Ammolite

Korite International's mechanized mining operations are fairly basic, involving the excavation of shallow pits with backhoes.

Ammolite comes from the fossil shells of the Upper Cretaceous disk-shaped ammonites Placenticeras meeki and Placenticeras intercalare, and (to a lesser degree) the cylindrical baculite, Baculites compressus. Ammonites were cephalopods, or squid-like creatures, that thrived in tropical seas until becoming extinct along with the dinosaurs at the end of the Mesozoic era.

The ammonites that form ammolite inhabited a prehistoric, inland subtropical sea that bordered the Rocky Mountains-this area is known today as the Cretaceous or Western Interior Seaway. As the seas receded, the ammonites were buried by layers of bentonite sediment. This sediment preserved the aragonite of their shelled remains, preventing it from converting to calcite.

Significant deposits of gem-quality ammolite are only found in the Bearpaw formation that extends from Alberta to Saskatchewan in Canada and south to Montana in the USA. The best grade of gem quality ammolite is along high energy river systems on the eastern slopes of the Rockies in southern Alberta. Most commercial mining operations have been conducted along the banks of the St. Mary River, in an area south of and between the town of Magrath and the city of Lethbridge. Roughly half of all ammolite deposits are contained within the Kainah (Kainaiwa) reserve, and its inhabitants play a major role in ammolite mining. Since its founding in 1979, Korite International has operated primarily within the reservation. The company maintains an agreement with the Kainah (Blood) tribe, with Korite International paying the tribe royalties based on how much land the company has mined.

Commercial extraction is mechanized but fairly basic: shallow open pits are dug with a backhoe and the excavated material is screened for its potential gem contents. The pits are further examined by hand, and commercial production is supplemented by independent persons who sell their surface-picked findings to Korite International and several other producers. Approximately 50% of the ammolite mined is suitable for jewelry.

The ammolite deposits are stratified into several layers: the shallowest of these layers, named the "K Zone", lies some 15 meters below the surface and extends 30 meters down. The ammolite within this layer is covered by siderite concretions and is usually cracked-this is the crush material. It is the most common and (generally speaking) the least valuable of ammolite. Beginning twenty meters below the crush material is the "Blue Zone"; ammolite from this zone, which extends 65 meters, is usually compressed with a thin layer of pyrite rather than siderite concretions. This is the sheet material; due to its depth it is rarely mined. It is also much less fractured, and therefore the more valuable type of ammolite.

Korite International had only mined 30 acres (120,000 m2) of the Kainah deposit by 2003.. As part of their agreement with the tribe, the company must refill areas once exhausted to mitigate environmental degradation. Prospectors who wish to mine ammolite deposits on Crown land must apply to the Alberta Department of Energy for a lease. These are not regularly offered and are very expensive.