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The Great Lakes Geologic Mapping Coalition—Working collaboratively to understand the geology of the Great Lakes Region

Introduction The Great Lakes Geologic Mapping Coalition (GLGMC), commonly referred to as the “Coalition,” is a partnership between the U.S. Geological Survey (USGS), the U.S. States of Illinois, Indiana, Michigan, Minnesota, New York, Ohio, Pennsylvania, and Wisconsin and the Canadian province of Ontario. The member States receive funding for geologic mapping work from the USGS National Cooperative Geologic Mapping Program (NCGMP), whereas Ontario participates as a nonfunded partner. The mission of the GLGMC is to produce three-dimensional (3D) geologic maps that depict unconsolidated sediments and near-surface bedrock in the Great Lakes region of North America. Geologic maps are the basis of most earth science investigations and help support resource exploration (energy, minerals, groundwater), natural hazard mitigation, infrastructure development, and land-use planning, all of which can be used to advance economic development and strengthen national security in the Great Lakes region. During the last few million years, the Great Lakes region has experienced repeated glacial advances and retreats, leaving behind extensive sediments, abundant natural resources, and widespread effects on the underlying bedrock geology (Swezey and others, 2022). Linked by shared histories of past glaciations, industrial agriculture, and legacy automotive, coal, steel, and manufacturing industries, the GLGMC member States collaborate to improve the understanding of the 3D distribution of the sediments overlying the region’s bedrock (fig. 1). Developing a comprehensive subsurface 3D framework of this glaciated terrain can provide earth science data to policymakers at all levels. These insights facilitate informed decisions on the exploration, use, and protection of vital resources, such as critical minerals, industrial materials, and aquifers, thereby supporting economic prosperity and the well-being of the citizens of this region. Since its inception in 1998, the Coalition has completed more than 100 geologic mapping projects across the Great Lakes region. Each project aims to deliver geologic maps, 3D datasets, and other information that improves understanding of the geology of the Great Lakes region, with an emphasis on economic and water resources. Key deliverables include 3D geologic maps and models typically portraying sediment thickness, often derived from top-of-bedrock and borehole data. These products are developed through a combination of fieldwork, subsurface modeling, and the collection and analysis of rock and sediment cores. To support Coalition goals, member States collaborate with scientists working on related STATEMAP, EDMAP, and FEDMAP projects. Coalition scientists also engage with Tribal Nations in the Great Lakes region to ensure that Tribal interests pertaining to Coalition work are addressed. Through this collaboration, the Coalition unites the efforts of State, Federal, and Tribal Nation stakeholders to advance geologic data production and enhance understanding of the geologic resources of the Great Lakes region.

Illinois, Indiana, Michigan, Minnesota, New York, ↗

Lead isotope compositions of Late Cretaceous and early Tertiary igneous rocks and sulfide minerals in Arizona: Implications for the sources of plutons and metals in porphyry copper deposits

Porphyry copper deposits in Arizona are genetically associated with Late Cretaceous and early Tertiary igneous complexes that consist of older intermediate volcanic rocks and younger intermediate to felsic intrusions. The igneous complexes and their associated porphyry copper deposits were emplaced into an Early Proterozoic basement characterized by different rocks, geologic histories, and isotopic compositions. Lead isotope compositions of the Proterozoic basement rocks define, from northwest to southeast, the Mojave, central Arizona, and southeastern Arizona provinces. Porphyry copper deposits are present in each Pb isotope province. Lead isotope compositions of Late Cretaceous and early Tertiary plutons, together with those of sulfide minerals in porphyry copper deposits and of Proterozoic country rocks, place important constraints on genesis of the magmatic suites and the porphyry copper deposits themselves. The range of age-corrected Pb isotope compositions of plutons in 12 Late Cretaceous and early Tertiary igneous complexes is 206 Pb/ 204 Pb = 17.34 to 22.66, 207 Pb/ 204 Pb = 15.43 to 15.96, and 208 Pb/ 204 Pb = 37.19 to 40.33. These Pb isotope compositions and calculated model Th/U are similar to those of the Proterozoic rocks in which the plutons were emplaced, thereby indicating that Pb in the younger rocks and ore deposits was inherited from the basement rocks and their sources. No Pb isotope differences distinguish Late Cretaceous and early Tertiary igneous complexes that contain large economic porphyry copper deposits from less rich or smaller deposits that have not been considered economic for mining. Lead isotope compositions of Late Cretaceous and early Tertiary plutons and sulfide minerals from 30 metallic mineral districts, furthermore, require that the southeastern Arizona Pb province be divided into two subprovinces. The northern subprovince has generally lower 206 Pb/ 204 Pb and higher model Th/U, and the southern subprovince has higher 206 Pb/ 204 Pb and lower model Th/U. These Pb isotope differences are inferred to result from differences in their respective post-1.7 Ga magmatic histories. Throughout Arizona, Pb isotope compositions of Late Cretaceous and early Tertiary plutons and associated sulfide minerals are distinct from those of Jurassic plutons and also middle Tertiary igneous rocks and sulfide minerals. These differences most likely reflect changes in tectonic setting and magmatic sources. Within Late Cretaceous and early Tertiary igneous complexes that host economic porphyry copper deposits, there is commonly a decrease in Pb isotope composition from older to younger plutons. This decrease in Pb isotope values with time suggests an increasing involvement of crust with lower U/Pb than average crust in the source(s) of Late Cretaceous and early Tertiary magmas. Lead isotope compositions of the youngest porphyries in the igneous complexes are similar to those in most sulfide minerals within the associated porphyry copper deposit. This Pb isotope similarity argues for a genetic link between them. However, not all Pb in the sulfide minerals in porphyry copper deposits is magmatically derived. Some sulfide minerals, particularly those that are late stage, or distal to the main orebody, or in Proterozoic or Paleozoic rocks, have elevated Pb isotope compositions displaced toward the gross average Pb isotope composition of the local country rocks. The more radiogenic isotopic compositions argue for a contribution of Pb from those rocks at the site of ore deposition. Combining the Pb isotope data with available geochemical, isotopic, and petrologic data suggests derivation of the young porphyry copper-related plutons, most of their Pb, and other metals from a hybridized lower continental crustal source. Because of the likely involvement of subduction-related mantle-derived basaltic magma in the hybridized lower crustal source, an indiscernible mantle contribution is probable in the porphyry magmas. Clearly, in addition, Pb was contributed from the local country rocks. This is most evident in sulfide minerals in veins that are late stage, hosted in Proterozoic gneiss, and/or peripheral to the porphyry copper deposit.

Economic Geology↗

Geochemical exploration for mineralized breccia pipes in northern Arizona, U.S.A.

Thousands of solution-collapse breccia pipe crop out in the canyons and on the plateaus of northern Arizona. Over 80 of these are known to contain U or Cu mineralized rock. The high-grade U ore associated with potentially economic concentrations of Ag, Pb, Zn, Cu, Co and Ni in some of these pipes has continued to stimulate mining and exploration activity in northern Arizona, despite periods of depressed U prices. Large expanses of northern Arizona are comprised of undissected high plateaus; recognition of pipes in these areas is particularly important because mining access to the plateaus is far better than to the canyons. The small size of the pipes, generally less than 600 ft (200 m) in diameter, and limited rock outcrop on the plateaus, compounds the recognition problem. Although the breccia pipes, which bottom in the Mississippian Redwall Limestone, are occasionally exposed on the plateaus as circular features, so are unmineralized near-surface collapse features that bottom in the Permian Kaibab and Toroweap Formations. The distinction between these two classes of circular features is critical during exploration for this unique type of U deposit.

Arizona↗

Re-Os sulfide geochronology of the Red Dog sediment-hosted Zn-Pb-Ag deposit, Brooks Range, Alaska

The Red Dog sediment-hosted deposit in the De Long Mountains of northern Alaska is the largest Zn producer in the world. Main stage mineralization is characterized by massive sulfide ore and crosscutting subvertical veins. Although the vein mineralization is clearly younger than the massive ore, the exact temporal relationship between the two is unclear. Re-Os geochronology of pyrite is used to determine the absolute age of main stage ore at Red Dog. A 10-point isochron on both massive and vein pyrite yields an age of 338.3 ?? 5.8 Ma and is interpreted to represent the age of main stage ore. The Re-Os data indicate that both massive and vein ore types are coeval within the resolution of the technique. Formation of the Red Dog deposit was associated with extension along a passive continental margin, and therefore the Re-Os age of main stage ore constrains the timing of rifting as well as the age of the host sedimentary rocks. Sphalerite from both massive and vein ore yields imprecise ages and shows a high degree of scatter compared to pyrite. We suggest that the Re-Os systematics of sphalerite can be disturbed and that this mineral is not reliable for Re-Os geochronology. ?? 2004 by Economic Geology.

Economic Geology↗

Mineral resources potential map of the Lost Cove and Harper Creek Roadless Areas, Avery and Caldwell counties, North Carolina

A geologic, geophysical, and geochemical investigation and a survey of mines, quarries, and prospects have been conducted to evaluate the mineral resource potential of the Lost Cove and Harper Creek Roadless Areas, Avery and Caldwell Counties, North Carolina. The study area lies within the Blue Ridge physiographic province and is predominatly underlain by Precambrian age plutonic and metasedimentary rocks of low metamorphic grade. All surface and mineral rights are Federally owned. Permit areas for uranium prospecting cover about 85 percent of the area. Uranium-rich rock in the Lost Cove and Harper Creek Roadless Areas occurs widely in the Wilson Creek Gneiss and to a minor extent in the Grandfather Mountain Formation. Vein-type deposits and other occurrences of uranium in foliated rocks in the Wilson Creek Gneiss have uranium resource potential. Speculative resources of uranium in vein-type deposits and in supergene-enriched foliated rocks are estimated to total 4 to 8 million pounds of U 3 O 8 . Mineral resources having low to moderate potential are gold and minerals of thorium, beryllium, niobium, and copper. Stone has a low economic potential; lead, molybdenum, and titanium have low resource potential. These conclusions are based on results of prospect examination, radiometric survey, geochemical survey of stream sediments, saprolite, and bedrock.

North Carolina↗

A special issue on volcanic centers as targets for mineral exploration; preface

NEPTUNE or Pluto? Since the days of Hutton and Werner, every generation of economic geologists has addressed this question in a new light. Most papers in this special issue deal with the thin and leaky roof of Pluto's underworld. It allows hot emanations from Hades to leak out, only to be quenched and diluted by waters percolating down from Neptune's realm.

Economic Geology↗

Agenda, extended abstracts, and bibliographies for a workshop on Deposit modeling, mineral resources assessment, and their role in sustainable development

Global demand for mineral resources continues to increase because of increasing global population and the desire and efforts to improve living standards worldwide. The ability to meet this growing demand for minerals is affected by the concerns about possible environmental degradation associated with minerals production and by competing land uses. Informed planning and decisions concerning sustainability and resource development require a long-term perspective and an integrated approach to land-use, resource, and environmental management worldwide. This, in turn, requires unbiased information on the global distribution of identified and especially undiscovered resources, the economic and political factors influencing their development, and the potential environmental consequences of their exploitation. The purpose of the IGC workshop is to review the state-of-the-art in mineral-deposit modeling and quantitative resource assessment and to examine their role in the sustainability of mineral use. The workshop will address such questions as: Which of the available mineral-deposit models and assessment methods are best suited for predicting the locations, deposit types, and amounts of undiscovered nonfuel mineral resources remaining in the world? What is the availability of global geologic, mineral deposit, and mineral-exploration information? How can mineral-resource assessments be used to address economic and environmental issues? Presentations will include overviews of assessment methods used in previous national and other small-scale assessments of large regions as well as resulting assessment products and their uses.

Open-File Report↗

Economic analysis of critical habitat designation for the desert tortoise (Mojave population)

The U.S. Fish and Wildlife Service emergency 1isted the Mojave population of the desert tortoise as endangered on August 4, 1989. The Mojave population formally was listed as threatened on April 2, 1990. The Endangered Species Act of 1973, as amended, requires that the economic benefits and costs and other relevant effects of critical habitat designation be considered. The Secretary of the Interior may exclude from designation areas where the costs of designation are greater than the benefits, unless the exclusion would result in extinction of the species. Desert tortoises are threatened by an accumulation of human-and disease-related mortality accompanied by habitat destruction, degradation, and fragmentation. Many desert tortoises are illegally collected for pets, food, and commercial trade. Others are accidentally struck and killed by vehicles on roads and highways or are killed by gunshot or vehicles traveling off-highway. Raven predation on hatchling desert tortoises has increased as raven populations in the desert have risen. An upper respiratory tract disease is suspected to be a major cause of mortality in the western Mojave Desert. This presumably incurable affliction presumably is thought to be spread through the release of infected tortoises into the desert. The Service has proposed designating critical habitat in nine counties within four states. The 12 critical habitat units encompass 6.4 million acres of land, more than 80% federally owned. This region is economically and demographically diverse. Most of the land is sparsely settled and characterized as a hot desert ecosystem. Major industries in the region include entertainment and lodging (primarily in Las Vegas), property development to accommodate the rapid population growth, and services. Millions of rural acres in the region are leased by the federal government for livestock grazing and used for mining. Overall economic benefits to the affected states derived from cattle and sheep grazing in the hot desert areas are minimal and, according to a recent U.S. General Accounting Office study (1991), local economies do not depend on the grazing of public lands for economic survival. The economic analysis describes the economy in 1990, prior to designation, and estimates the effects of designation. The report estimates those incremental effects attributable to critical habitat designation. Impacts attributable to listing the species were not considered in this analysis. Although critical habitat units have been designated in nine counties, two counties are omitted from the economic analysis because of the small proportion of critical habitat acreage they include. Three key activities (cattle grazing, mineral extraction, and off-road vehicle use) were studied in detail. Even if livestock grazing and commercial off-road racing events were eliminated in the proposed critical habitat units, the potential incremental regional economic impacts would be extremely small. The findings in the report do not include the assumption that mining would be eliminated from critical habitat units, but rather that consultation may result in added mitigation and/or relocation of features. Studies show that society will realize benefits from preservation of species and ecosystems. Survey-based studies confirm that benefits exist and are substantial in size, although these benefits often are not measured in traditional economic markets. The total benefit to society of desert tortoise preservation includes several components. Biodiversity in the Mojave and Colorado Deserts will be improved, some recreation values may increase, and gains in intrinsic value will be realized. Critical habitat designation should result in the loss of fewer than 425 total jobs in the seven counties. These include 340 direct ranching jobs and 85 indirect jobs in other industries. This estimated employment loss will not be permanent for most laborers, it is anticipated that over 85% will be reemployed within two years. The economic consequences of designating critical habitat includes reduced ranch profits in the seven counties of $4,470,000 [the estimated permanent decrease in ranch profits, capitalized at 10% for a 50-year period, in accordance with the methodology of River, et al. (1978)]. Second, the federal government will compensate allottees with a one-time payment estimated at $376,000 for the loss of permanent improvements to grazing lands (pending BLM administrative decisions of partially affected allotments). Finally, discontinuing grazing fees will result in an annual reduction of $170,000 in collected grazing fees that are divided among range improvements, the Federal Treasury, and local governments.

California, Nevada↗

Quantitative approaches to characterizing natural chemical weathering rates

Silicate minerals, constituting more than 90% of the rocks exposed at the earth’s surface, are commonly formed under temperature and pressure conditions that make them inherently unstable in surficial environments. Undoubtedly, the most significant aspect of chemical weathering resulting from this instability is the formation of soils which makes life possible on the surface of the earth. Many soil macronutrients in this “critical zone” are directly related to the rate at which primary minerals weather (Huntington, 1995; Chadwick et al., 2003). Chemical weathering also creates economically significant ore deposits, such as those for Al and U (Samma, 1986; Misra, 2000), as well as potentially releasing high concentrations of toxic trace elements such as Se and As (Frankenberger and Benson, 1994). Silicate weathering is a significant buffer to acidification caused by atmospheric deposition (Driscoll et al., 1989) and from land use practices (Farley and Werritty, 1989). Atmospheric CO 2 levels have been primarily controlled by the balance between silicate weathering and the rate of volcanic inputs from the Earth’s interior, a relationship which may explain long-term climate stability (Ruddiman, 1997)

Book chapter↗

Remnant colloform pyrite at the haile gold deposit, South Carolina: A textural key to genesis

Auriferous iron sulfide-bearing deposits of the Carolina slate belt have distinctive mineralogical and textural features-traits that provide a basis to construct models of ore deposition. Our identification of paragenetically early types of pyrite, especially remnant colloform, crustiform, and layered growth textures of pyrite containing electrum and pyrrhotite, establishes unequivocally that gold mineralization was coeval with deposition of host rocks and not solely related to Paleozoic tectonic events. Ore horizons at the Haile deposit, South Carolina, contain many remnants of early pyrite: (1) fine-grained cubic pyrite disseminated along bedding; (2) fine- grained spongy, rounded masses of pyrite that may envelop or drape over pyrite cubes; (3) fragments of botryoidally and crustiform layered pyrite, and (4) pyritic infilling of vesicles and pumice. Detailed mineral chemistry by petrography, microprobe, SEM, and EDS analysis of replaced pumice and colloform structures containing both arsenic compositional banding and electrum points to coeval deposition of gold and the volcanic host rocks and, thus, confirms a syngenetic origin for the gold deposits. Early pyrite textures are present in other major deposits of the Carolina slate belt, such as Ridgeway and Barite Hill, and these provide strong evidence for models whereby the sulfide ores formed prior to tectonism. The role of Paleozoic metamorphism was to remobilize and concentrate gold and other minerals in structurally prepared sites. Recognizing the significance of paragenetically early pyrite and gold textures can play an important role in distinguishing sulfide ores that form in volcanic and sedimentary environments from those formed solely by metamorphic processes. Exploration strategies applied to the Carolina slate belt and correlative rocks in the eastern United States in the Avalonian basement will benefit from using syngenetic models for gold mineralization.

Economic Geology↗

Quartz veins in the Ouachita mountains of Arkansas and Oklahoma (Their relations to structure, metamorphism, and metalliferous deposits)?

An important chapter of the total geologic history of the Ouachita Mountains is revealed by the quartz veins and crystals. These and the associated minerals are hydrothermal deposits of probable magmatic origin, formed during the closing stage of the mid-Permsylvanian orogeny. The metalliferous deposits of the Ouachita Mountains appear to have been formed at the time of the quartz vein deposition. This /act should be considered in dating the lead and zinc mineralization in other areas of the Mississippi Valley region. © 1943 Society of Economic Geologists, Inc.

Arkansas, Oklahoma↗

Merumite occurrence in Guyana

Merumite was discovered with associated diamonds and gold in 1937 in gravels of the Merume River in Guyana. It was described as essentially a hydrous chromium oxide that contains more than 80 percent Cr2Oa. Milton and Chao in 1958 found it to be a complex aggregate, mainly eskolaite (Cr2Oa) with five or more new chromium minerals which have recently been identified. The deposit is unique. The richest gravel, averaging several ounces merumite per cubic yard, extends about 2 miles along the base of an east-dipping (35°) ridge of sandstone and ash beds, perhaps an outlier of the Precambrian Roraima Formation that forms bold mountainous scarps a few miles south. No chromium mineralization has been observed in the ridge or anywhere in the region, other than the merumite in the placer gravel. Merumite commonly occurs as grains a few millimeters across, but specimens as large as 10 cm have been found. Almost all the merumite is in rounded grains, many with broken worn edges, indicating wear in transport. Granular gold is enclosed in merumite, as is chromian pyrophyllite. Many merumite grains have impressions, and some contain crystals, of doubly terminated "needle" quartz. Water-worn gorceixite, rutile, tourmaline-quartz fels, jasper, euhedral glassy quartz (as much as several centimeters long), and fragments of basaltic rock accompany merumite at all localities; rarely, gold and diamonds are associated in the placers. Merumite was probably derived from a local moderate-temperature hydrothermal deposit possibly formed in the adjacent sandstone-volcanic ash bed from solutions related to local ash deposits and massive gabbro-dolerite intrusive bodies in the Roraima Formation. If the deposit was formed at depths of less than a few thousand feet, erosion may have reached it and re-deposited the merumite and accompanying resistant minerals, mostly'quartz and jasper, in local stream beds. © 1969 Society of Economic Geologists, Inc.

Merume River↗

Direct dating of mineralization at Goldfield, Nevada, by potassium-argon and fission-track methods

Potassium-argon dating of hypogene alunite and K-mica from hydrothermally altered rocks at Goldfield, Nevada, yields mineralization ages of 20 to 21 m.y., in good agreement with a mineralization age established by potassium-argon dating of unaltered premineralization and postmineralization volcanic units. Premineralization volcanic units that are pervasively propylitized cannot be dated by the potassium-argon method but yield zircon fission-track ages, and in several cases yield concordant apatite fission-track ages. Two samples from premineralization units yield apatite ages concordant with the age of mineralization established by potassium-argon geochronometry, reflecting annealing of the apatite during the hydrothermal episode.Potassium-argon dating of supergene alunite samples yields imprecise ages in the range 9 to 12 m.y. that probably record the first exposure of their hydrothermally altered host rocks to oxidizing conditions. Potassium-argon dating of postmineralization basalts and silicic tuffs interbedded with conglomerates bearing altered rock clasts shows that the altered area was eroded nearly to present topographic levels by 11 m.y. ago, at which time it was covered by basalt flows now represented only by scattered remnants. Apatites from premineralization volcanic units give fission-track ages of 20 m.y. or more, indicating that no significant thermal event has affected altered rocks at Goldfield since mineralization took place.

Nevada↗

xygen isotope, aeromagnetic, and gravity anomalies associated with hydrothermally altered zones in the Yankee Fork mining district, Custer County, Idaho

Epithermal Ag-Au vein and disseminated deposits in the Yankee Fork district are hosted in altered volcanic rocks having low delta 18 O values, low magnetic susceptibilities, low remanent magnetizations, and relatively high densities. These isotopic and physical quantities provide sensitive indices of rock alteration that can be contoured over areas that are much larger than zones of strong visible alteration. Such contour maps reveal a marked spatial association between the ore deposits, the steepest delta 18 O gradients, and the perimeter of zones where the rocks have extremely low total magnetizations. The oxygen isotope results indicate that the ore zones coincide with steep gradients in temperature and water/rock ratio in two fossil hydrothermal convective systems that involved fluids derived from Tertiary meteoric waters. Our magnetic measurements suggest that these same high-gradient zones also coincide with oxidation-reduction boundaries. Low aeromagnetic intensities and positive Bouguer anomalies are also associated with the altered zones in the Yankee Fork district. The intensities of these geophysical features are consistent with the size of the altered zones and with the contrast in physical properties between altered and unaltered rocks. Contour maps of the magnetic and isotopic properties of host rocks should find application in exploration for a variety of types of hydrothermal ore deposits, as well as in the study of ore controls and conditions of mineralization.

Economic Geology↗

The Coastal and Marine Geology Program of the U.S. Geological Survey

Nearly half of all Americans live within an hour's drive of an ocean, the Gulf of Mexico, or the Great Lakes. The U.S. coastal oceans are an economically vital transportation, commercial and recreational resource. They provide food, energy, and minerals for the entire Nation: on a global scale, they harbor critical habitat for important animal and plant species.

Fact Sheet↗

Analyses and description of geochemical samples, Peters Mountain Wilderness Study Area, Giles County, Virginia

Semiquantitative emission spectrographic analyses for 64 elements on 43 stream sediment and 73 rock samples from Peters Mountain Wilderness Study area, Giles County, Virginia, are reported here in detail. Locations for all samples are in Universal Transverse Mercator (UTM) coordinates. Brie[ descriptions of rock samples are also included. Rocks analysed are mostly sandstone. Samples of hematitic sandstone of the Rose Hill Formation and limonite-cemented sandstone of the Rocky Gap Sandstone contain high values of iron; these rocks are submarginal iron resources. Some of the same iron-rich samples have a little more barium, copper, cobalt, lead, silver, and/or zinc then average sandstone, but they do not suggest the presence of economic deposits of these metals. No other obviously anomalous values related to mineralized rock are present in the data.

Open-File Report↗

Analyses and description of geochemical samples, Mill Creek Wilderness Study Area, Giles County, Virginia

Semiquantitative emission spectrographic analyses for 64 elements on 62 stream sediment and 71 rock samples from Mill Creek Wilderness Study area, Giles County, Virginia, are reported here in detail. Locations for all samples are given in Universal Transverse Mercator (UTM) coordinates. Brief descriptions of rock samples are also included. Rocks analysed are mostly sandstone. Samples of hematitic sandstone of the Rose Hill Formation and limonite-cemented sandstone of the Rocky Gap Sandstone contain high values of iron; these rocks are submarginal iron resources. Some of the same iron-rich samples have a little more barium, copper, cobalt, lead, silver, and/or zinc then is in average sandstone, but they do not suggest the presence of economic deposits of these metals. No other obviously anomalous values related to mineralized rock are present in the data.

Open-File Report↗