Gold Deposits at the Zortman-Landusky Mine

This page was written by Erin Klauk as part of the DLESE Community Services Project: Integrating Research in Education.

Figure 1: Schematic illustration of geologic environments in which hydrothermal gold deposits form. Arrows show sources of water thought to have formed these deposits. Details

Gold is one of the most economically important metals produced. As of 1991, more than 83% of gold consumption went into jewelry, 6% was used for medals and official coins, 6% was used in electronic equipment, 2.2% was used for dental materials, and 2.8% was consumed in a variety of industrial applications. These markets support an annual gold production of about 2,200 tons worth almost $25 billion ([Kesler, 1994] ).

There are many types of gold deposits (more info) including vein deposits, contact deposits, replacement deposits, disseminated ore and placers. A few miles south of the Fort Belknap Indian Reservation lies the Zortman-Landusky mine where gold is found in intrusion related breccia-hosted deposits in the Little Rocky Mountains. In this type of deposit, gold mineralization is found in magmatic-hydrothermal or phreatomagmatic pipe-like breccias (Figure 1) associated with the intrusion of stocks, plugs, sills or dikes into a wide variety of host rocks ranging in age from Precambrian to Tertiary (Mineral Commodity Report 14: Gold (more info) ).

During the Tertiary, igneous activity domed the Little Rocky Mountains and formed the laccolithic intrusion, dikes and sills where gold-silver mineralization occurred. The gold is found in small quartz veins that are concentrated in large fissure zones of shattered and altered rock. Some low-grade gold is also present in auriferous pyrite disseminated locally in the syenite and other intrusive rocks. In a few areas gold occurs in higher-grade replacement deposits in limestone (Status of Mineral Resource Information for the Fort Belknap Indian Reservation, Montana ( This site may be offline. ) ).

To further investigate gold deposits at the Zortman-Landusky mine, follow the links below.

Gold, 6.8 cm high, Homestake Mine, Salmon River District, Siskiyou County. Details

Gold Deposits

Resources containing information on gold deposits.

  • Au-Ag-Te Vein Deposits. This resource is a part of the USGS document entitled "Preliminary Compilation of Descriptive Geoenvironmental Mineral Deposit Models". This chapter of the document describes gold, silver and tellurium vein deposits. Topics include a summary of relevant geologic, environmental, and geophysical information, geologic factors that influence potential environmental effects, and environmental signatures. (more info)
  • Descriptive Model of Au-Ag-Te Veins. This USGS document provides a summary of characteristics of gold-silver-tellurium vein deposits. The data includes the geological environment of the deposits such as rock types, textures, age ranges, depositional environment, tectonic setting, and associated deposit types. The deposit description includes information about mineralogy, texture/structure, alteration, ore controls, and weathering. Also included is a list of examples where these vein deposits are found. (more info)
  • Mineral Commodity Report 14: Gold. This Institute of Geological and Nuclear Sciences document provides information about gold mining and production. Topics include types of ores and minerals, properties, formation, uses, price, world production and consumption, ore processing and refining, production, reserves, and future trends. Also described are the different ways that gold deposits form including placer deposits, mesothermal deposits, banded iron formation deposits, epithermal gold-silver deposits, intrusion related breccia-hosted deposits, and by-product gold. Detailed examples from around the world are given for each type of gold deposit. (more info)
  • Technical Resource Document: Extraction and Beneficiation of Ores and Minerals Volume 2: Gold. This EPA document provides detailed information about the gold mining industry in terms of the wastes associated with gold mining and processing. The report briefly characterizes the geology of gold ores and the economics of the industry. Specific information from EPA site visits is included for the Brewer Mine, Colosseum Mine, Nerco Minerals Cripple Creek, and the Newmont Gold Company in Nevada. (more info)
  • Mineral Resources, Economics and the Environment. [Kesler, 1994] This is a textbook that covers mineral resources, economics and the environment. (citation and description)

Gold Deposits at the Zortman-Landusky Mine

Resources containing information on the gold deposits at the Zortman-Landusky mine.

  • Status of Mineral Resource Information for the Fort Belknap Indian Reservation, Montana. This U. S. Department of Energy paper describes the status of mineral resources for the Fort Belknap Indian Reservation in north central Montana. The paper discusses the general geology, stratigraphy, Precambrian metamorphic rocks, tertiary intrusive rocks, and structural geology of this area, as well as information about energy resources, metallic mineral resources, and nonmetallic mineral resources. Also included in this paper are a number tables and figures that illustrate the topics discussed. ( This site may be offline. )
  • Zortman, Landusky: Gold. This Porter GeoConsultancy webpage describes the gold and silver deposits at Zortman and Landusky in north central Montana. Early exploration and development history of gold and silver in the Little Rocky Mountains, and the geology of this area are discussed. (more info)
  • Gold Deposits of Zortman-Landusky, Little Rocky Mountains, Montana. [Hastings, 1988] This paper discusses the history and development of the gold deposits of the Zortman-Landusky mine. Geologic information is provided about the regional setting, structural geology, sedimentary rocks, igneous rocks, and ore deposits of the area. Many figures accompany the text, including a geologic map and stratigraphic column of the Little Rocky Mountains. (citation and description)
  • Geochemistry of Porphyry-Hosted Au-Ag Deposits in the Little Rocky Mountains, Montana. [Wilson and Kyser, 1988] This article discusses the geochemistry of the gold and silver deposits in the Little Rocky Mountains, specifically at the Zortman and Landusky mining areas. (citation and description)

For ideas on how to use these webpages in a classroom, a Study Guide is provided.