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J. P. Albers

Publications and source records attributed to J. P. Albers.

15 recordsLinked to original sources
USGS1985

Regional setting and new information on some critical geologic features of the West Shasta district, California

The West Shasta massive sulfide district is in the easternmost of a series of accreted island-arc and oceanic crust terranes that comprise the Klamath Mountains. A sequence of submarine volcanic rocks of predominantly Early Devonian age is the principal component of the island-arc terrane in which the sulfide deposits are hosted. The Copley Greenstone, consisting mainly of andesitic and basaltic pillow lavas and breccias totaling at least 1,800 m in thickness, is the oldest rock unit in the sequence. It is overlain and also intruded by dikes of the Balaklala Rhyolite. Northeast of the West Shasta district, greenstone also overlies the Balaklala Rhyolite, suggesting that a major greenstone unit may overlie potentially mineralized rhyolite east of the district. However, recent studies have shown that the complex relations in that area can be explained by folding.The Balaklala sequence consists of silicic flows, breccias, and tuffs having a maximum thickness somewhat in excess of 1,000 m. The Balaklala has been divided by Kinkel et al. (1956) into three units: a lower nonporphyritic to slightly porphyritic unit containing large amounts of breccia and tuff; a middle unit characterized by rhyolite containing quartz phenocrysts 1 to 4 mm in diameter but also containing a complex assortment of tuff, breccia, and pyritic massive sulfide bodies in its upper part; and an upper unit typically containing dark quartz phenocrysts in excess of 4 mm in diameter. Much of the lower part of the upper unit is pyroclastic material, whereas most of the upper part of the unit appears to be a massive volcanic-flow rock. At least half a dozen eruptive centers for the Balaklala Rhyolite are identified, three of them within an area measuring 17 X 3 km that constitutes the limits of the former mining district.The youngest unit in the arc sequence is the Kennett Formation consisting of black shale and chert containing radiolarians, which indicate fairly deep-water deposition in its lower part, and limestone containing a shallow water fauna of probable Middle Devonian age in the upper part. A 400-m.y.-old trondhjemite stock, named the Mule Mountain stock, intrudes the Copley Greenstone and Balaklala Rhyolite and is considered to be essentially coeval with these volcanic units.The pyritic massive sulfide deposits occur in clusters of individual bodies owing in large part to disruption by postmineral faults. The deposits are stratigraphically confined to the upper part of the subhorizontal middle unit of the Balaklala, and their horizontal distribution is here interpreted to have been controlled by an extensional tectonic regime that prevailed during Early Devonian time. The major geologic evidence for such a regime is the marked preferred elongations exhibited by the distribution of the afore-mentioned eruptive centers, the eight or nine massive sulfide clusters in the district, and the geometrically similar distribution of the clusters in relation to each other. The preferred directions of elongation in both the detailed and broader senses may be generalized to N 20 degrees to 25 degrees E, N 37 degrees E, N 60 degrees to 80 degrees E, and N 40 degrees to 60 degrees W. The three northeast trends dominate throughout the district, whereas the northwest trend is evident mainly in the northern part and is more speculative. The major deposit clusters fall at intersections of the major trends, some of which may have been grabens. Trend intersections having no known deposits may be good exploration targets in localities where the stratigraphically favorable middle unit of the Balaklala is still present.

Economic Geology↗
USGS1985

Geology of the Brick Flat massive sulfide body, Iron Mountain cluster, West Shasta district, California

The Brick Flat massive sulfide body is one of a group of 8 individual bodies that constitute the Iron Mountain cluster in the S part of the West Shasta district. Before they were separated by postmineral faulting, 5 of the 8 sulfide bodies formed a single large deposit about 1375 m long with a mass of some 23 million metric tons. The pyritic Brick Flat sulfide body is one of the 5 faulted segements of this deposit. The Brick Flat massive sulfide lies within medium phenocryst rhyolite that is characteristic of the ore-bearing middle unit of the Balaklala Rhyolite. It is interpreted to be downfaulted a vertical distance of 75 to 85 m from the Old Mine sulfide-gossan orebody along the N-dipping Camden South fault. It is bounded in turn on its N side by another parallel fault, the Camden North, which drops the orebody down another 75 m to the level of the Richmond orebody. -from Author

Economic Geology↗
USGS1985

The plumbotectonics of the West Shasta mining district, eastern Klamath Mountains, California

The tectonic setting comprising the West Shasta mining district has often been compared with that of primitive island arcs. Concentrations of uranium, thorium, and lead and lead isotope compositions were determined for Devonian ores and rocks of the West Shasta district, eastern Klamath Mountains, California, to help evaluate the tectonic classification. The lead isotope pattern is found to be complex. From comparison of the data with those on younger ores and rocks in the region and with those isotopic patterns found in modern tectonic terranes, however, a number of conclusions are possible. A lead isotope point for the Devonian oceanic mantle is now well established from this study on the West Shasta district. This isotopic composition is in agreement with that suggested by Slawson in 1983--i.e., from a sample of massive sulfide ore from the Golinsky deposit--with a 206 Pb/ 204 Pb of 17.830, a 207 Pb/ 204 Pb of 15.450, and a 208 Pb/ 204 Pb of 37.313. If the Devonian mantle is analogous to the modern mantle, the determined value is probably at the more radiogenic end of the Devonian oceanic mantle array.Some samples of volcanic rocks and ores that have elevated values of 207 Pb/ 204 Pb and 208 Pb/ 204 Pb indicate that subducted pelagic sediments or interaction of the magmas with other sediments downsection have been involved to varying degrees in the generation of magmas. The high ratios were not attained by addition of lead to the volcanic rocks or ores during subsequent magmatic events, such as intrusion of the Permian Pit River stock to the east or of the Cretaceous Shasta Bally batholith that crops out to the south and west and may underlie part of the district. Some values of 207 Pb/ 204 Pb are sufficiently high as to suggest that West Shasta may have developed nearer a continent than was previously supposed. Lead isotope data for Quaternary volcanic rocks are somewhat more radiogenic than for Cretaceous ores and plutonic rocks. Permo-Triassic ores are again a bit less radiogenic. The isotopic differences between the Permo-Triassic and Quaternary data could be accounted for by a value for 238 U/ 204 Pb of 10.42 in common source material. Using this value of 238 U/ 204 Pb to calculate even further back to 400 m.y., the resulting ratios are found to fall very close to the "best value" for the lead isotope mixing line between the Devonian mantle and pelagic sediments. We interpret this intersection to be the "mean value" for the assimilated Devonian sediment lead--18.250 for 206 Pb/ 204 Pb and 15.582 for 207 Pb/ 204 Pb. As deduced for the lead isotope composition for the Devonian mantle at this location, the pelagic sediment, lead isotope composition also is toward the more radiogenic end of the values expected for pelagic sediments in the Devonian. Lack of sediments in the observed volcanic section of the West Shasta district suggests a submerged volcanic-arc setting (as interpreted by others for the Troodos and Samail ophiolites) rather than an island-arc situation (such as the Green Tuff area of Japan) or an incipient spreading ridge setting (that might have grown to be a subaerial Iceland). The elevated values of 207 Pb/ 204 Pb for some samples suggest a submerged volcanic are whereas the exceedingly low values of thorium--which is not easily mobilized during alteration events--for both basaltic andesites and plagiorhyolites is suggestive of depleted source material such as is found for most oceanic spreading centers. Elevated values of 207 Pb/ 204 Pb are exceedingly rare in midocean ridge basalts and low contents of thorium are known in island arcs, so a submerged volcanic arc is the preferred interpretation. Some similarity exists between the 206 Pb/ 204 Pb values of Devonian ores having elevated values of 207 Pb/ 204 Pb and those of the Permo-Triassic ores of the East Shasta district, as mentioned by Slawson in 1983. This similarity is now confirmed to be a coincidence. We find it due first of all to some incorporation of sediment lead in the magmas, followed later by some migration of radiogenic lead--probably locally derived--into the ores during subsequent events. Because there was some postdepositional lead migration into the ores, some migration of copper also into the ores cannot be excluded. Lead, especially radiogenic lead, however, is more mobile than copper. As the migrating lead is deduced to have been locally derived from the observed section rather than exotically derived, any copper added was probably locally derived also.

Economic Geology↗
USGS1981

A lithologic-tectonic framework for the metallogenic provinces of California

The lithologic-tectonic framework of California developed principally during Mesozoic time when various terranes of oceanic crust and island-arc crust were accreted to older sialic crust, resulting in westward growth of the continent. Emplacement of great batholithic masses of granitoid rocks cutting all these crustal types also took place during the Mesozoic period. The discrete tectonostratigraphic terranes that resulted from these events and subsequent Tertiary and Quaternary volcanic events are characterized by specific types of metallic mineral deposits or, in some terranes, by the virtual absence of deposits. Lead-silver-zinc replacement-type deposits are common in the Paleozoic carbonate terrane in the eastern part of the state and occur sporadically elsewhere in the miogeoclinal and cratonal terranes but are absent from the oceanic and island-arc terranes. The vast majority of contact metasomatic tungsten deposits, including all the large ones, are in pendants of miogeoclinal rocks in the Sierra Nevada batholith, but the important Atolia deposits reside in granitoid rocks that invade oceanic terrane. Molybdenum distribution closely follows that of tungsten. All the large contact metasomatic iron deposits in California are in craton and miogeoclinal terranes, but sparse small deposits of this type also occur in island-arc terranes of the northern Sierra Nevada and eastern Klamath Mountains. Lode gold deposits, although widely scattered, show a marked preference for oceanic and island-arc terranes that have been invaded by granitoid plutons. All the major deposits, including late Tertiary bonanza deposits such as Bodie, are in such terranes. It appears that magmatic processes were responsible for mobilizing and transporting the gold, but the metal was perhaps derived from the eugeosynclinal rocks, notably the mafic volcanics. Most mercury deposits are found in the Coast Ranges, where they commonly occur in silica-carbonate rock, an alteration product of serpentinite. The deposits appear to be spatially related to the Coast Range thrust, and the source of the mercury may have been sedimentary rocks of the underlying Franciscan assemblage. Epigenetic mineralization occurred at several different times during the Mesozoic, and again during Miocene and Pliocene time. The timing of mineralization events and the distribution of various deposit types indicate that no broad-scale zoning of epigenetic deposits exists around the Sierra Nevada batholith.Syngenetic deposits are represented mainly by massive sulfides, chert-associated manganese, and chromite. The massive sulfide deposits, with one exception, are restricted to island-arc terranes, and nearly all of these deposits are in silicic volcanic rocks. They are interpreted to be syngenetic with the enclosing rocks, although some redistribution of metals may have occurred after the original deposition. The deposits occur in volcanic sequences of at least five different ages ranging from Early Devonian to Late Jurassic or Early Cretaceous and, along with their enclosing rocks, were probably formed at some distance from their present sites. Chert-associated manganese deposits occur mainly in exotic blocks of oceanic crust in melange and probably formed in fairly deep ocean environments. Chromite is confined to ultramafic rock, much of which occupies suture zones separating various accreted terranes.

Economic Geology↗
USGS1972

Massive sulfide copper deposits of the Ergani-Maden area, Southeastern Turkey

The copper deposits of the Ergani-Maden area, in the Taurus Mountains of southeastern Turkey, have been a major source of copper for more than 4,000 years. The area is underlain by gently dipping mudstones interlayered with mafic volcanic rocks and lenticular beds of limestone, mainly of Eocene age. The layered rocks were intruded and slightly metamorphosed by large masses of gabbro and related mafic rocks that are now largely serpentinized. The copper deposits are in an east-trending belt about 20 km long, near the center of which is the town of Maden. A broad geochemical anomaly extends north-northwest and south-southeast from this belt, its axis passing near Maden. Near the mines the main igneous mass has a gently dipping roof and steep sides. Around and south of Maden, where the mass has barely been unroofed, are many roof pendants and remnants of sedimentary and volcanic material. One of these contains the largest mine in the area--the Ana Yatak. The largest deposit, the Aria Yatak ore body, occurs in a canoe-shaped pendant of mudstone that occupies atrough about 1 km long and 1/2 km wide in the top of the intrusive. The present vertical extent is about 170 meters. In the central and western parts of the trough the mudstone is chloritized and partly replaced by ore minerals. The main ore body is about 550 X 300 X 50 m in maximum dimensions. It consists mainly of pyrite and chalcopyrite, and locally it contains abundant magnetite or pyrrhotite. The gangue consists predominantly of chlorite, smaller amounts of quartz, and very minor amounts of calcite and barite. The massive sulfide ore body is underlain by "impregnation ore" in which veinlets and irregular small masses of sulfides are embedded in chloritized mudstone. A zone rich in supergene chalcocite, corellite, and bornite lies between the sulfide mass and the well-developed gossan in many places, and this was extensively mined in ancient times. The Mihrap Dagi mine, about 1 km northwest of the Aria Yatak deposit, is also near a contact between the intrusive and the sedimentary rock. It too contains a massive sulfide ore body accompanied by chloritized rock, but it contains little "impregnation ore." In the Ergani-Maden area, ore deposition followed a long history of sedimentation, lithification, faulting, intrusion of mafic igneous rocks, serpentinization, and further faulting, and was part of a broad-scale introduction of metal into the sedimentary, extrusive, and intrusive rocks. Thus it is epigenetic. The major ore bodies are fracturecontrolled replacement masses. Adularia which occurs in veins a few hundred meters south of the main sulfide ore bodies is inferred to have formed contemporaneously with the sulfide and shows a potassium-argon age of 31.5 +/- 0.8 m.y. If this inference is correcthe deposits formed during middle Oligocene or slightly later.

Ergani-Maden↗
USGS1971

Primary and secondary sulfates at Goldfield, Nevada

High S-34 values for primary alunites (formed during hydrothermal phase) replacing plagioclase and groundmass of altered volcanic rocks, secondary alunite veins (formed during supergene alteration) with S-34 values near zero permil

Nevada↗
USGS1968

Summary of regional evidence for right-lateral displacement in the western Great Basin

Right-lateral displacement of 80 to 120 miles across the western Great Basin is indicated by the consistent disruption of sedimentary facies and thickness trends of formations ranging in age from late Precambrian to Mesozoic. Some of this displacement occurs as fault slip and some as a more pervasive large-scale drag (oroflexural bending).

California, Nevada↗