Maps showing locations of mines and prospects in the Butte ...

[Pages:156]U.S. DEPARTMENT OF THE INTERIOR U.S. GEOLOGICAL SURVEY

Maps showing locations of mines and prospects in the Butte 1?X2? quadrangle, western Montana

By James E. Elliott, Jeffrey S. Loen, Kristine K. Wise,

and Michael J. Blaskowski

Pamphlet to accompany MISCELLANEOUS INVESTIGATIONS SERIES

MAP I-2050--C

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U.S. DEPARTMENT OF THE INTERIOR U.S. GEOLOGICAL SURVEY

Maps showing locations of mines and prospects in the Butte 1?X2? quadrangle, western Montana

By James E. Elliott, JeffreyS. Loen, Kristine K. Wise,

and Michael J. Blaskowski

Pamphlet to accompany MISCELLANEOUS INVESTIGATIONS SERIES

MAP I-2050-C

Any use of trade names in this publication is for descriptive purposes only and does not imply endorsement by the U.S. Geological Survey

CONTENTS

Introduction 1 History of mining 5 Production 8 Data sources and methods of compilation 9 Mines and prospects 9 References cited 10 Sources of data for tables 1 and 2 119 FIGURES 1. Index map showing locations of mining districts and geographic areas, Butte 1?X2?

quadrangle, Montana 2 2. Principal structures and plutons of the Sapphire thrust plate 5 TABLES 1. Location and description of mines and prospects, Butte 1?X2? quadrangle,

Montana 12 2. Production data for mining districts and geographic areas, Butte 1?X2? quadrangle,

Montana 114 3. Mineral deposit types and frequency of each type, Butte 1?X2? quadrangle,

Montana 124 4. Alphabetical index of site names, Butte 1?X2? quadrangle, Montana 125

III

INTRODUCTION

The Butte 1?X2? quadrangle, in west-central Montana, is one of the most mineralized and productive regions in the U.S. Mining districts in this quadrangle, which include the world famous Butte or Summit Valley district, have produced a variety of metallic and nonmetallic mineral commodities valued at more than $6.4 billion (at the time of production). Because of its importance as a mineral producing region, the Butte quadrangle was selected for study by the U.S. Geological Survey under the Conterminous United States Mineral Assessment Program (CUSMAP). Under this program, new data on geology, geochemistry, geophysics, geochronology, mineral resources, and remote sensing were collected and synthesized for the purpose of mineral resource assessment. The field?and laboratory studies were supported, in part, by funding from the Geologic Framework and Synthesis Program and the Wilderness Program. This map is one of a number of reports and maps on the Butte 1?X2? quadrangle. Other publications resulting from this study include U.S. Geological Survey (USGS) Miscellaneous Investigation Series Maps 1-2050-A (Rowan and Segal, 1989), 1-2050-B (Rowan and others, 1991), 1-2050-D (Elliott and others, in press a), and 1-2050-E (Elliott and others, in press b); Miscellaneous Field Studies Maps MF-1925 (Wallace, 1987); and Open-File Reports 86-292 (Wallace and others, 1986) and 86-0632 (Elliott and others, 1986).

Data for a total of 1,128 mines, prospects, and mineral occurrences have been compiled for the Butte quadrangle. Mineralized sites are distributed throughout the quadrangle, but most sites are concentrated in principal mining districts; 78 percent of the mines, prospects, and occurrences are clustered in 47 established mining districts and the remaining 22 percent are more widely scattered in 23 geographic areas (fig. 1). The locations of mines and prospects are shown on the map and figures 3-14 and a brief description of each site and of each district or geographic area is in table 1 (in pamphlet), which is arranged by mining district or geographic area. The description of each site includes site number, name and alternate name(s), location by latitude and longitude, commodities present, geologic setting of site, type of deposit, size of production, type and extent of mine workings, and sources of data. Data for this report were obtained from the U.S. Geological Survey Mineral Resource Data System (MRDS; formerly known as the Computerized Resource Information Bank (CRIB)), from many published and unpublished sources, and from new geologic field work.

GEOGRAPHIC SETTING

The Butte quadrangle is bounded by latitudes 46? and 47? Nand longitudes 112? and 114? W (fig. 1). The city of Butte is in the southeastern part; Helena, the state capital of

Montana, is on the eastern edge; and Missoula is near the northwestern comer of the quadrangle. Most of the quadrangle is in Granite, Powell, Lewis and Clark, and Jefferson Counties, and smaller parts are in Missoula, Ravalli, Deer Lodge, and Silver Bow Counties. The quadrangle includes numerous mountain ranges separated by intermontane valleys. The continental divide trends nearly south through the eastern part of the quadrangle to a point near Butte, and then trends generally west near the southern boundary of the quadrangle. East of the divide, drainage is to the Missouri River, and west of the divide, to the Clark Fork, which heads in the vicinity of Butte.

GEOLOGIC SETTING

The Butte quadrangle contains igneous, metamorphic, and sedimentary rocks that range in age from Proterozoic to Quaternary. Proterozoic, Paleozoic, and Mesozoic sedimentary rocks are abundant and widespread, as are Cretaceous and Tertiary plutonic rocks; the latter are in the cores of most mountain ranges and are associated with metamorphic rocks. Volcanic and volcaniclastic rocks of Cretaceous and Tertiary ages are found mostly in mountain ranges in the eastern and northern parts of the quadrangle. Intermontane basins are filled by Tertiary and Quaternary sedimentary rocks and surficial deposits.

The sedimentary record begins with rocks of the Belt Supergroup that were formed during Middle Proterozoic time when part of the Belt basin occupied the region of the Butte quadrangle; clastic and carbonate rocks of the Belt Supergroup have a total thickness of at least 52,000 ft in the quadrangle. Mafic dikes and sills were intruded into the Belt rocks, probably during Late Proterozoic time. During Paleozoic time, near-shore and shallow-water carbonate and carbonate-bearing clastic sediment was deposited and the resulting strata have a total thickness of about 7,900 ft; Paleozoic strata are mainly in the north, central, and northeastern parts of the quadrangle. Mesozoic sedimentary rocks were deposited in a foreland basin that accumulated about 22,000 ft of clastic and carbonate strata in the central part of the quadrangle and about 7,900 ft of equivalent strata in the northeastern part of the quadrangle.

In Late Cretaceous time, numerous stocks and several batholiths were emplaced at mesozonal and epizonal depths. The Boulder, Idaho, Sapphire, and Philipsburg batholiths, composed of monzogranite and granodiorite, and numerous stocks of diorite, granodiorite, and monzogranite were intruded during Late Cretaceous time. Hydrothermal activity during and following the waning stages of magmatism formed a variety of mesothermal and epithermal mineral deposits. The Elkhorn Mountains Volcanics, of Late Cretaceous age, are found as roof pendants and along the margins of the Boulder batholith and probably represent early extrusive phases of the magma which later formed the Boulder batholith.

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