Mineral surveys by the Geological Survey and the Bureau of Mines of Bureau of Land Management Wilderness Study Areas

First printing 1983 Second printing 1984

This report describes the Interior Department's wilderness program, with particular emphasis on the joint mineral surveys conducted by the U.S. Geological Survey (USGS) and U.S. Bureau of Mines, of those public lands recommended by the Bureau of Land Management (BLM) as suitable for inclusion in the National Wilderness Preservation System.

Mineral surveys by the Geological Survey and the Bureau of Mines were originally mandated by the Wilderness Act of 1964 (Public Law 88-577), which, together with subsequent legislation, dealt with national forests managed by the U.S. Forest Service of the Department of Agriculture and with certain lands managed by the Department of Interior including wildlife refuges. The Federal Land Policy and Management Act of 1976 (Public Law 94-579), informally referred to as FLPMA, in turn instructed the Bureau of Land Management to review all public lands under its jurisdiction and determine their suitability or nonsuitability for wilderness designation. Areas recommended as suitable for wilderness designation by the BLM are also required to have mineral surveys conducted by the Geological Survey and the Bureau of Mines.

Although the program is not yet completed, the Geological Survey and the Bureau of Mines have conducted mineral surveys of 44 million acres of national forest and other lands in the 19 years since passage of the Wilderness Act. Individual mineral resource potential reports on hundreds of areas already have been published. In addition, a summary volume containing about 330 brief reports on the mineral resource potential of the areas studied as part of the Forest Service wilderness program will be published in 1984.

Mineral surveys of BLM wilderness study areas are not undertaken until the final stages of the BLM wilderness review. Consequently, this program is just barely underway, and thus far mineral assessments have been completed for about 2 million acres. About 6.5 million acres remain to be surveyed.

The Wilderness Act of 1964 established a "National Wilderness Preservation System for the permanent good of the whole people, and for other purposes." The Wilderness System consists of federally owned lands preserved and protected in their natural condition so that present and future generations can have the benefits of an enduring resource of wilderness. Only Congress can designate Federal lands as part of the Wilderness System.

Section 2(c) of the 1964 Wilderness Act defines wilderness as follows:

The Federal Land Policy and Management Act instructs the Bureau of Land Management on how it is to manage the 470 million acres of land under its jurisdiction and sets forth provisions for wilderness review in section 603. In summary, section 603 directs the Secretary of the Interior and the BLM (1) to review all roadless public land areas of 5,000 acres or more and roadless islands having wilderness characteristics as defined by section 2(c) of the 1964 Wilderness Act; (2) to determine their suitability or nonsuitability for wilderness designation; (3) to have the Geological Survey and Bureau of Mines conduct mineral surveys of areas preliminarily recommended as suitable for inclusion in the National Wilderness Preservation System to determine mineral values that may be present; and (4) to report wilderness recommendations to the President no later than October 21, 1991. The President must report his final recommendations to Congress no later than 2 years after the 1991 deadline, and Congress will decide if an area is to become wilderness. The BLM is presently studying 23.1 million acres for wilderness under section 603 of FLPMA and 0.1 million acres under section 202 as described below.

Section 603(a) of FLPMA, which describes mineral surveys, is as follows:

In addition to the 23.1 million acres being studied for wilderness under Section 603 of FLPMA, the BLM is also considering another approximately 150,000 acres (0.1 million) under Section 202 of FLPMA the BLM's general planning authority. Most of these study areas are smaller than 5,000 acres and are contiguous to existing or proposed wilderness areas. Mineral surveys will also be conducted for those Section 202 wilderness study areas which are preliminarily recommended as suitable for wilderness designation.

Natural or primitive areas have been specifically designated as such by the BLM and are protected under special management regulations. As described in Section 603(a) of FLPMA, wilderness recommendations on the 55 existing natural and primitive areas were to be made to the President by July 1, 1980. These natural and primitive areas were called Instant Study Areas (ISA's). Their study and evaluation became one of BLM's highest priorities, and it was necessary to start mineral surveys of certain ISA's soon after passage of the 1976 Act. At BLM's request, the Geological Survey and the Bureau of Mines began studies in 1978 on 23 ISA's, 10 of which were subsequently recommended for wilderness (fig. 1). Another 10 are deferred-study ISA's whose suitability/nonsuitability recommendations will be made as part of the multiple-use plan process. Three of the ISA's on which mineral surveys were done subsequently were recommended as unsuitable. As of May 1983, the only BLM-managed area to be recommended to Congress by the President for inclusion in the National Wilderness Preservation System is the Aravaipa Canyon Primitive Area in Arizona (frontispiece).

A special priority for study was also given in FLPMA to the California Desert Conservation Area (CDCA), which is covered separately by section 601. Because of their unique character and fragile environment, the desert lands required immediate planning and management attention. Of the 25 million acres in the desert region, the BLM manages half. The comprehensive, longrange management plan called for in section 601 was completed and submitted to Congress on September 30, 1980. As part of the comprehensive desert plan, BLM identified 5.7 million acres in 138 areas that met its criteria for wilderness. Of these, 2.2 million acres in 47 areas were foundthrough a multiple-use planning process to be suitable for wilderness and thus to require mineral surveys by the Geological Survey and the Bureau of Mines (fig. 2). In 1983, BLM is amending its original comprehensive plan for the California Desert; in the amended plan some suitable areas may be dropped from wilderness consideration and others added.

The BLM published a "Wilderness Inventory Handbook" in September 1978 in which it outlined policy, direction, and procedures for its wilderness inventory. The wilderness review consists of three phases: an inventory phase, a study phase, and a reporting phase.

The inventory phase was divided into an initial inventory, which used existing data to identify land that lacked wilderness characteristics, and an intensive inventory, which focused on lands for which field work was needed in order to conclude whether they had wilderness characteristics. The initial inventory covered the entire 470 million acres administered by the BLM; 296 million acres clearly lacked wilderness characteristics and were dropped from further consideration (fig. 3).

The intensive inventory of the remaining 174 million acres was completed in November 1980. As a result, another 150 million acres were dropped from wilderness consideration, and 23.2 million acres consisting of 928 areas possessing wilderness characteristics as defined by section 2(c) of the Wilderness Act were identified and considered as wilderness study areas.

The BLM recognizes wilderness as a resource deserving consideration with other resources in land use planning, and it recognizes wilderness useage as use to be considered in the framework of multiple-use of public lands. The BLM will recommend for wilderness designation those wilderness study areas for which they determine through their planning process (into which public opinion is incorporated) that wilderness is the most appropriate use of the land and the resources associated with land.

Federal land management agencies have been and are being required to consider huge acreages for wilderness. This requirement has necessitated the development of a data-gathering process that includes minerals data so that all potential uses of the many tracts under consideration may be evaluated. The Roadless Area Review and Evaluation (RARE II) process met this need for the Forest Service, and the BLM has developed the Geology, Energy, and Minerals (GEM) process to collect minerals data. Such data are part of the information on which suitability/nonsuitability recommendations are based (fig. 4).

BLM's wilderness review guidelines assure that any recommendations related to an area's suitability for wilderness will reflect thorough consideration of any identified resources as well as mineral resource potential. The GEM process, which includes a literature search and collection of available information to develop a data base for each wilderness study area, and an analysis of known mineral resources of the area based on this data, was initiated in 1981 and implemented in 1982. The GEM studies may include limited field verification, but they are not field-oriented. They are designed primarily to use existing data adequate for assessment of resource potential, in contrast to the joint mineral surveys on the suitable wilderness study areas by the Geological Survey and Bureau of Mines required by section 603 of FLPMA. The results of the Geological Survey/ Bureau of Mines mineral surveys are considered by the Secretary of the Interior prior to making his final wilderness recommendations to the President. The information contained in the mineral potential reports may change an area previously recommended as suitable to a nonsuitable recommendation.

In the reporting phase of the wilderness review, suitability recommendations, together with environmental statements, Geological Survey/Bureau of Mines mineral resource potential reports, and other data, are sent to the President who submits them to Congress. The reporting process for "suitable" recommendations the only areas required by law to have mineral surveys is shown in figure 4.

Because virtually all the obvious mineral deposits have been identified, the search for new resources requires current technology combined with a highly sophisticated and thorough knowledge of geologic science. Mineral discoveries such as the gold at Sutler's Mill and the oil of Spindletop occurred at a time when our mineral wealth was much easier to find.

Mineral deposits form by numerous geologic processes and in almost any geologic environment, but unique factors are required to concentrate minerals sufficiently to form a mineral deposit. These deposits are distributed unevenly in the crust of the Earth. Mineral exploration and also mineral resource appraisals may involve many considerations, some of which are listed below:

The existence of most economic mineral deposits depends upon a complex sequence of geologic conditions and processes. For example, a producible oil deposit results from sedimentary rocks rich in organic matter; high enough heat to convert the organic matter to oil; a geologic structure or formation that enables the oil to migrate from the source rock to a porous reservoir rock; and a rock that seals the reservoir and holds the oil in place so that it accumulates in quantity. Extractable mineral deposits of both fuel and nonfuel minerals occur in localized areas within broad mineralized regions such as the Colorado Mineral Belt, the Viburnum Trend in Missouri, the Coeur d'Alene District in Idaho, or the San Juan Basin. As new technologies and new geologic concepts are developed on how mineral deposits form, areas previously poorly explored or unexplored must be reevaluated. For example, the deeper parts of the Rocky Mountain Overthrust Belt had largely been forgotten until 1975 when discovery of the Pineview Field touched off a drilling boom and led to the discovery of billions of barrels of oil and trillions of cubic feet of natural gas. New technologies can make previously unimportant minerals highly valuable; examples include uranium, natural gas, tantalum, and lithium. Wilderness legislation requires mineral surveys in order to provide a basis for making balanced judgments regarding mineral resources and wilderness resources. The Geological Survey and the Bureau of Mines were given the responsibility of conducting wilderness mineral surveys for the following reasons: (1) all facets of mineral resources work are within the joint responsibility of these two agencies; (2) their thoroughness and objectivity has been established and is accepted by those involved in the wilderness recommendation process; and (3) both agencies already possess the extensive technical expertise required to conduct such surveys.

The level of data collected in the course of these mineral surveys is a compromise between cost and time and the amount of detail. This compromise is acceptable to many individuals and organizations interested in the wilderness recommendation process, although the minerals industry would like more detailed surveys. More detailed studies would require costly physical exploration normally undertaken by the private sector, and less detailed studies would not be thorough enough to provide the level of detail needed by BLM and other agencies in determining whether an area should or should not be recommended for wilderness.

The distinction between work done by the Geological Survey and that done by the Bureau of Mines as part of the joint mineral surveys is that the studies of the Geological Survey cover the entire area and are designed to provide a reasonable scientific basis for estimating the possibilities of future mineral discoveries, whereas those of the Bureau of Mines are more site specific and are primarily concerned with the evaluation of individual mines and known mineralized areas. The Geological Survey studies are oriented toward determining geologic units and structures, possible environments of mineral deposition, and presence of geochemical and geophysical anomalies.

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they contribute information on geology that will be useful as resource needs of the United States change. As technology presents new demands and new opportunities, resource appraisals of some areas will need to be updated and conclusions reevaluated.

The Geological Survey uses studies in three separate earth science disciplines geology, geochemistry, and geophysics to evaluate the mineral potential of wilderness study areas. The amount of involvement of each of these disciplines is designed to fit the specific needs for data in each wilderness study area or group of closely spaced areas.

The Geological Survey for many years has been conducting mineral resource appraisals for different purposes and at different scales, and its methods are constantly evolving. A workshop, organized for the purpose of improving mineral resource appraisal techniques, was held in Denver, Colorado, in December 1979. Daniel R. Shawe compiled the results in Geological Survey Circular 845, "U.S. Geological Survey Workshop on Nonfuel Mineral Resource Appraisal of Wilderness and CUSMAP1 Areas," published in 1981; the conclusions reached in the workshop are summarized on page 13 of that report:

In Circular 845, Shawe also includes a comprehensive description of the methodology used by the Geological Survey in mineral resource appraisals, including specific application of each of the three disciplines, which are only briefly described here. The results of these studies are integrated and used to understand past and present geologic environments, surface and subsurface geology, processes acting in the area that might produce resources, and to find mineralized systems.

Geologic maps, which show the distribution, age, and relationships of rock units as they crop out at the surface, provide the foundation required for interpretation of all other data collected for mineral assessment (fig. 5). Regional geologic maps produced in other programs portray regional features, including the presence of rocks that may provide an environment for mineral deposits, major structures, and trends associated with mineral deposits. They show the location of structures, including folds, faults, and fractures, that may be factors in localizing processes of mineralization. Examination of the terrane for direct evidence of mineralization, such as presence of ore minerals and altered rock, is an integral part of geologic mapping. Geologic maps enable us to trace geologic evolution in time and space and to define a sequence of geologic environments. They provide a basis for the interpretation of geochemical and geophysical data and enable prediction of mineral resource potential.

A map scale of 1:62,500 (1 inch=l mile), 1:24,000 (1 inch=2,000 feet), or a scale intermediate between these two depending on the geologic complexity of the individual area, is used in order to show adequate detail (fig. 6).

Greatly improved means of data collection and improved laboratory techniques for analyzing field data, such as isotopic age determinations to provide time frames for volcanic and plutonic rocks and mineralized systems, have enhanced the application of geologic mapping in mineral resource evaluation. Geologic maps display data in an organized fashion. The kinds of features that are now known to be related to mineralization and that we can discern from geologic maps have increased dramatically. Included among these features are ophiolites, calderas and ring fracture zones, and hot spring systems with disseminated gold and silver.

Exploration geochemistry is the systematic collection of samples and the measurement of their elemental composition to identify clues to geologic environments that may be favorable for the occurrence of mineral deposits. Analytical geochemical techniques directly measure abundance of elements which, if found in anomalous concentrations (greater than normal throughout the region), may indicate the proximity of a mineral deposit or ore buried at depth. Geochemical studies, combined with geologic mapping and geophysical surveys as an integrated program, have become increasingly important in mineral resource appraisals since the late 1940's.

Virtually all exposed ore deposits were discovered long ago by prospectors; any remaining exposed and most near-surface ore deposits have been discovered more recently by geologists using geologic mapping techniques and drilling. Consequently, emphasis had to shift from the search for exposed mineral deposits to the search for evidence, such as geochemical anomalies, that indicates the possible presence of environments favorable for mineral deposits. With this change in emphasis, geochemistry has become increasingly important. Current resource appraisal must also be directed to studying the potential for mineral commodities not considered in earlier days, such as barite, lithium, and rare-earth elements, and geochemistry is an invaluable aid in detecting these elements.

The geochemical techniques used by the Geological Survey have evolved over more than 30 years. Because of the increased effectiveness of geochemistry in mineral appraisal in recent years, its usefulness in the BLM wilderness program, which is just getting underway, is greater than it was in the first decade of the Forest Service program. The costs that result from extensive use of geochemistry are warranted because of its effectiveness in ferreting out favorable environments for ore deposits that might otherwise be overlooked.

In a reconnaissance geochemical study, one stream sediment sample site per square mile is visited. Two samples are collected at each stream site one for analysis of the sediment and one for panning to concentrate the heavy minerals. Rock samples are also collected to determine the normal background concentrations of elements in the local bedrock and to serve as examples of atypical material related to mineralization. Water samples are collected from any springs or seeps present in the map area because they may carry elements dissolved from concealed mineralized rocks. Other sample media used in geochemical studies include soils, oxide-coatings, vegetation, and soil gases. A variety of sample media are used to find signs of mineralization that might be missed if only one medium were used. An area found to have anomalously high concentrations of elements will be revisited and sampled in greater detail.

Strict quality control is maintained by the Geological Survey in sample preparation and analysis of geochemical samples. All stream sediments, heavy-mineral concentrates, and rock samples are analyzed for 31 elements by the six-step semiquantitative emission-spectrographic technique, and any other more sophisticated unique analysis that is required. Mobile laboratories are taken to some field locations to enable prompt detailed follow-up work in areas showing anomalous concentrations of elements.

The first step in interpretation is preparation of the geochemical anomaly maps, element by element, and the second step is determining whether or not a pattern of anomalous elements is related to mineralization. In order to determine if geochemical anomalies are significant with respect to concealed deposits, several factors must be evaluated including the geology of the area, trace element abundances in the normal rock types of the area, elemental associations in the various types of mineral deposits, climatic conditions, character of weathering, mobility of the elements in the surface and near-surface environments, characteristics of the sample media used, sampling methods, and analytical methods used to obtain the data. The geologic setting of the area, including the rock types, weathering, and structural geology is especially important in evaluating geochemical anomalies as signs of mineralization. Significant geochemical anomalies are related to accumulations of minerals, which may constitute either economic or subeconomic deposits at present. Nonsignificant anomalies may be related to industrial contamination such as old mine tailings or to high-background source rocks.

Airborne geophysical techniques such as magnetic surveys and remote-sensing are extremely useful in mineral resource appraisals because they can be used to detect differences or contrasts in the Earth's crust that are not detectable by direct observation of the Earth's surface. Geophysical methods also allow geologists to ascertain the shape of rock bodies beneath the Earth's surface. Geophysical surveys can help pinpoint certain areas with abnormal properties that may be related to mineral deposits.

Because in mineral surveys of BLM wilderness areas the areas to be studies are defined, geophysics is used selectively the technique judged to provide the most useful data is applied. The most commonly used geophysical method is an aeromagnetic survey. Aeromagnetic data provide information about buried intrusive rocks and altered zones that may be associated with mineralization. Aeromagnetic surveys can be done rapidly and at a relatively low cost. As in geochemical studies, anomalous areas, in this case areas with abnormal magnetic properties, may be followed with a detailed ground survey.

A second geophysical reconnaissance technique, one that is most useful in semiarid and arid terranes, is a remote-sensing technique using Landsat data to detect and map limonite (iron oxides). The limonite maps are field checked to determine whether or not the limonite results from weathering of hydrothermally altered rocks. The resulting hydrothermal alteration maps, combined with geochemical data, help locate buried mineralization. This remote-sensing approach has been used effectively in the mineral surveys of the California Desert Conservation Area.

Other geophysical methods include gravity surveys (density of rocks) and electrical profiling (electrical properties of rocks), including magnetotellurics and DC electrical resistivity. Reconnaissance methods provide maps of different physical properties that augment geological surface mapping; such maps are most useful when they include data on several different physical properties.

Site-specific geophysical methods include gravity and magnetics as well as induced polarization (IP), electromagnetic, radiometric, and selfpotential methods. The electrical and radiometric methods are used in some cases as direct indicators of mineralization. These methods are used very selectively in mineral surveys of wilderness study areas because they are expensive.

Bureau of Mines studies of wilderness study areas involve collection of data on current and past mining activities and field examination of mines and Of the 23.2 million acres of BLM wilderness study areas, 1.0 million acres are Instant Study Areas, 5.7 million acres are in the CDCA, and 16.5 million acres are other areas. The status of mineral surveys of these different categories of wilderness study areas is shown in figure 9.

Mineral surveys have been completed on all suitable ISA's. No changes were necessary in the suitability recommendations as a result of the mineral surveys because the areas were not found to have significant mineral potential. Mineral surveys have also been completed in 10 of the deferred-study ISA's. Less than 0.4 million acres of ISA's remain under consideration for wilderness (fig. 1).

Of the 5.7 million acres of wilderness study areas in the CDCA, 2.2 million acres were recommended for wilderness as part of the 1980 comprehensive desert plan (fig. 2). As of May 1983, mineral resource potential reports have been published on about half a million acres, mineral surveys are in progress on about 1.5 million acres, and surveys will be started on the remaining half a million acres in fiscal year 1984. The schedule for completion of mineral survey reports in the CDCA is shown in figure 2.

Wilderness study areas other than ISA's and the CDCA total 16.5 million acres. Of this total, mineral surveys are currently completed or underway on 1.1 million acres (fig. 10). BLM tentatively recommended 2.0 million areas as suitable at the end of fiscal year 1982.'The Geological Survey and Bureau of Mines will begin mineral surveys of these areas in fiscal year 1984.

About 9.9 million acres remains under review by BLM. In January 1983, the Directors of the Geological Survey, the Bureau of Mines, and the Bureau of Land Management signed a Memorandum of Understanding (MOU) concerning the mineral surveys of wilderness study areas. The MOU, shown in Appendix A, covers policy and operational procedures and also includes the schedule by which BLM will complete review of the remaining 9.9 million acres.

On the basis of past experience, it has been assumed for budget and workload purposes that not more than 65 percent of these remaining 9.9 million acres, or about 6.5 million acres, will be recommended as suitable. If this is the case, mineral surveys of the remainder of the program can be completed according to the schedule shown in table 1 and can meet the mandated 1991 completion date for the program. In accordance with the Memorandum of Understanding (see appendix A), the Bureau of Land Management has, as of May 1983, provided the Geological Survey and Bureau of Mines with the total number of acres (2.3 million) for which mineral surveys are to be started in fiscal year 1985 for use in the budget process.

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