Quartz Hill Research Articles

Assembling the world’s type shallow subduction complex: Detrital zircon geochronologic constraints on the origin of the Nacimiento block, central California Coast Ranges

Temporal and spatial patterns in the architecture of the Franciscan Complex provide valuable insights into the subduction processes through which such patterns arise. The Nacimiento Franciscan belt is an allochthonous sliver of subduction assemblages in the central California Coast Ranges displaced either: (1) from southern California by >300 km of Neogene dextral slip along the San Andreas fault system or (2) from central California to southern California and back again, by >500 km of Late Cretaceous–Paleocene sinistral slip along the Sur-Nacimiento fault followed by San Andreas–related motion. New U-Pb detrital zircon data from 20 (meta)clastic samples indicate that the Nacimiento Franciscan section was assembled between ca. 95 and 80 Ma. Abundant Cretaceous (particularly Late Cretaceous) and diminishing amounts of Jurassic and Proterozoic zircon grains point to a southern California origin for Nacimiento Franciscan protoliths, precluding significant sinistral strike-slip along the Sur-Nacimiento fault. Furthermore, the suite of detrital zircon ages reported here bears a strong resemblance to new and existing data from subduction complexes in southern California that were emplaced during Laramide shallow subduction (i.e., Sierra de Salinas, Portal Ridge, Quartz Hill, Rand, San Emigdio, and Tehachapi schists). Hence, the Nacimiento Franciscan is distinct from Franciscan rocks in central and northern California and more likely represents an outboard element of the Late Cretaceous southern California low-angle subduction system. Upon restoring the Nacimiento block to its Late Cretaceous position, an inboard-younging trend is apparent in the composite Nacimiento–southern California schist belt, suggesting that progressively younger accretionary materials were underplated farther inboard by tectonic erosion. We posit that arc and forearc elements absent from southern California were removed by a combination of physical and tectonic erosion attending shallow subduction, interleaved in the subduction complex, and recycled into the mantle. Steepening of the Laramide slab was marked by a phase of crustal extension in the overriding plate. During this phase, the Sur-Nacimiento fault likely functioned as a segment of a low-angle normal fault system spanning the southern Sierra Nevada batholith to the Nacimiento accretionary system.

Quartz Hill, Alaska: a case history of engineering and environmental requirements for STD in the USA : C. A. Hesse & D. V. Ellis, Marine Georesources & Geotechnology, 13(1–2), 1995, pp 135–182

The Quartz Hill molybdenum prospect, with an estimated tailings disposal rate of up to 80,000 tons per day, was developed through preliminary engineering design, environmental impact assessments, and permit applications during the 1970s and 1980s. The intent was to meet the stringent environmental requirements of several federal and state regulatory agencies. The case history of mine development, extending over two decades, provides a unique set of details usable by future large‐scale coastal and island mine prospects in the U.S. and elsewhere. Two fjords provided options for submarine tailings disposal (STD) with conventional deaeration and seawater mix chamber. An outfall was designed, and would be located, to produce a density current descending to fjord bottom. Innovative modeling of near‐field and far‐field tailings dispersal, and resuspension potential, was developed and applied. Of about $102,000,000 invested on the development, approximately $31,000,000 was given to environmentally related work. F...

Provenance and Depositional Setting of Paleozoic Chert and Argillite, Sierra Nevada, California

ABSTRACT The Shoo Fly Complex, the remnants of an early to middle Paleozoic subduction system, contains the Culbertson Lake allochthon. Included in the Culbertson Lake allochthon are the post-Cambrian and pre-Upper Devonian Quartz Hill, Toms Creek, and McMurray Lake cherts. Geochemical data derived from these three units plot on the Fe2O3/TiO2 versus Al2O3/(Al2O3 + Fe2O3) and Lan/Cen versus Al2O3/(Al2O3 + Fe2O3) discrimination diagrams within either the continental margin-island arc field, or that part of the pelagic field overlapping the continental margin-island arc field. These relationships a e consistent with the presence of argillaceous turbidites interstratified with radiolarite, and suggest a relatively distal continental-island arc setting where muddy turbidity currents episodically interrupted pelagic deposition. Specimens from the Quartz Hill and Toms Creek cherts with Al2O3/TiO2 values > 20 make up Group I samples, whereas specimens with Al2O3/TiO2 values < 10 are classified as Group II samples. The Al2O3/TiO2 ratios of Group II specimens suggest derivation from mafic rock. Mean Th/Sc and Th/U values, as well as LREE-enriched patterns, are consistent with this interpretation, and indicate a source area dominated by alkalic seamount or ocean island material. The Al2O3/TiO2 ratios of Group I samples indicate a source area with an average andesitic to rhyodacitic composition. Chondrite-normalized REE distribution patterns, as well as mean Th/Sc and Th/U value , support such an interpretation. Samples from the McMurray Lake chert have Al2O3/TiO2 values ranging between 19 and 28, and REE patterns characterized by LREE enrichment, negative Eu anomalies, and slightly fractionated HREE patterns. These features, along with mean Th/Sc and Th/U values, indicate a source area dominated by old upper continental crust. The location of the source area(s) supplying material to cherts and argillites of the Culbertson Lake allochthon is unknown. However, existing tectonic models commonly portray the source of old upper continental crustal material in the Shoo Fly Complex as being located somewhere along the western North American continental margin, whereas the source of island-arc debris is portrayed as being located in a fringing arc system. Our data suggest that a relatively high-standing seamount or ocean island probably resided on the subducting oceanic plate. Thus, our work supports the idea that Al, Fe, Ti, Th, Sc, and the REEs in chert and argillite deposited in proximal continental-island arc settings can be used to assess the characteristics of sources supplying particulate matter to ancient t ench systems.

Heavy metals in seaducks and mussels from misty fjords national monument in Southeast Alaska

Quartz Hill, in Misty Fjords National Monument near Ketchikan, Alaska, is the site of a proposed molybdenum-producing mine. To provide baseline data for use in post-development comparisons, we analyzed tissues of Barrow's goldeneyes (Bucephala islandica), common mergansers (Mergus merganser), and blue mussels (Mytilus edulis) for seven heavy metals that could potentially be released into the environment as a result of mining operations. Specimens were collected in 1980, 1981, and 1982 from two fjords likely to be used for discharge of tailings from the proposed mine and from two control fjords. Concentrations of arsenic, cadmium, copper, chromium, molybdenum, lead, and zinc were measured in soft tissues of mussels and in kidney, liver, and muscle of birds. The highest mean concentrations of metals found in bird tissues were 55.7 ppm dry weight cadmium in kidneys and 154 ppm dry weight zinc in livers of Barrow's goldeneyes. Concentrations of several metals in blue mussels differed among seasons and locations, but the most significant finding in mussels was a maximum mean cadmium concentration of 9.6 ppm dry weight, a level higher than normally found in undisturbed areas. With the exception of 104 ppm dry weight cadmium in the kidney of one common merganser and 12.7 ppm dry weight lead in the kidney of another, concentrations of other metals in seaduck and mussel tissues were low, consistent with what would be expected for a pre-development environment. Molybdenum was found in low concentrations (<10 ppm dry weight) in all avian kidney samples and most liver samples, but was not detected in blue mussels.

Quartz hill, Alaska: A case history of engineering and environmental requirements for STD in the USA

The Quartz Hill molybdenum prospect, with an estimated tailings disposal rate of up to 80,000 tons per day, was developed through preliminary engineering design, environmental impact assessments, and permit applications during the 1970s and 1980s. The intent was to meet the stringent environmental requirements of several federal and state regulatory agencies. The case history of mine development, extending over two decades, provides a unique set of details usable by future large‐scale coastal and island mine prospects in the U.S. and elsewhere. Two fjords provided options for submarine tailings disposal (STD) with conventional deaeration and seawater mix chamber. An outfall was designed, and would be located, to produce a density current descending to fjord bottom. Innovative modeling of near‐field and far‐field tailings dispersal, and resuspension potential, was developed and applied. Of about $102,000,000 invested on the development, approximately $31,000,000 was given to environmentally related work. F...

Tectonic control and fluid evolution in the Quartz Hill, California, lode gold deposits

At Quartz Hill, in the Klamath Mountains of northern California, gold-bearing quartz-carbonate-pyrite-chlorite-sericite veins occupy reactivated moderately southeast-dipping faults that originally formed synchronously with the transcrustal Soap Creek Ridge fault. Geophysical evidence suggests that the Soap Creek Ridge fault dips shallowly eastward to a depth of approximately 14 km, where it intersects a major crustal suture zone that joins layered accreted oceanic crust to crystalline continental crust. Gold mineralization occurs in the footwall along the linear trace of this fault. CO 2 -rich fluids reacted with wall rock to form alteration zones containing pyrite-siderite, sericite-ankerite, and chlorite-calcite. Microthermometric studies reveal coexisting high-salinity (11-16 wt % salt) aqueous and CO 2 -rich (13-51 mole % CO 2 ) inclusions that homogenize at temperatures greater than 285 degrees C. These inclusions probably represent the unmixing of a parent fluid that was metamorphic in origin. Low-salinity (0-6 wt % salt) inclusions with variable CO 2 concentrations (0-9 mole % CO 2 ) homogenize at temperatures from 170 degrees to 270 degrees C. These inclusions are likely to have formed from the mixing of hot, saline, CO 2 -rich solutions with cooler, less saline fluids of meteoric origin.K-Ar analyses of two size fractions of hydrothermal sericite from a Quartz Hill mine yielded concordant dates of 145.8 + or - 3.0 and 147.7 + or - 2.8 Ma and probably represent the age of mineralization. Similarities in tectonic setting, local structural control, host rocks, fluid inclusion properties, and alteration and vein mineralogy suggest that the Early Cretaceous gold mineralization in the Sierra Nevada foothills was equivalent to the ore-forming episode at Quartz Hill and throughout the Klamath Mountains.A tectonic model for ore genesis consistent with thermochemical, geophysical, structural, and geochronological data is that hydrothermal solutions were derived from subducting oceanic plates by devolatilization reactions associated with prograde metamorphism. These CO 2 -rich fluids migrated upward through a crustal suture zone and were channeled along a transcrustal fault. Deposition occurred in response to pressure fluctuations within brittle fault zones. Important changes in Farallon-North American convergent plate motion occurred at 150 and 133 Ma. The synchronism of these plate motion changes with regional tectonic activity and gold mineralization suggests a genetic relationship. These plate motion changes produced crustal-scale tectonic responses, which generated fluids and created pathways for ore fluid transport.

Individual and combined toxicity of manganese and molybdenum to mussel, Mytilus edulis, larvae.

During toxicity testing of mine tailings from the proposed Quartz Hill molybdenum mine, which will be situated near Ketchikan, Alaska, the metals molybdenum (Mo) and manganese (Mn) showed evidence of leaching from the tailings. In order to determine whether these metals could be responsible for toxicities observed previously, Mytilus edulis mussel larvae bioassays (ASTM 1984) were conducted with these metals, both individually and in combination. The results of the bioassays showed that these metals could account for only a very small proportion of the tailings toxicity.

Acute toxicity of mine tailings to four marine species

Acute toxicity bioassays were conducted on mine tailings produced by pilot plant testing for the proposed Quartz Hill molybdenum mine, which will be situated near Ketchikan, Alaska. Tailings bioassays were conducted in seawater with juvenile coho salmon ( Oncorhynchus kisutch), mussel larvae ( Mytilus edulis), infaunal amphipods ( Rhepoxynius abronius), and euphausiids ( Euphausia pacifica). The same general range of mine tailings concentrations was acutely toxic to all four test species with acute effects observed between 61 000 to 277 000 mg l −1 (wet wt) tailings solids (range of 95% confidence limits for LC 50 and EC 50 values). Chemical analyses of bioassay test solutions and leaching test solutions were conducted for metals (including Cd, Cu, Pb, Zn, Mn and Mo), EPA Priority Pollutant base/neutral organics, and more general parameters such as sulphate, nitrate/nitrite, cyanides, phosphate and ammonia. Parameters possibly contributing to the observed toxicity were complex contaminant mixtures including total suspended solids and heavy metals. The present study provides information related to the marine disposal of mine tailings and shows that these mine tailings present a relatively low level of acutely toxic effects.

A heat-flow reconnaissance of southeastern Alaska

Heat flow was measured at nine sites in crystalline and sedimentary rocks of southeastern Alaska. Seven of the sites, located between 115 and 155 km landward of the Queen Charlotte – Fairweather transform fault, have an average heat flow of 59 ± 6 mW m−2. This value is significantly higher than the mean of 42 mW m−2 in the coastal provinces between Cape Mendocino and the Queen Charlotte Islands, to the south, and is lower than the mean of 72 ± 2 mW m−2 for 81 values within 100 km of the San Andreas transform fault, even farther south. This intermediate value suggests the absence of significant heat sinks associated with Cenozoic subduction and of heat sources related to either late Cenozoic tectono-magmatic events or significant shear-strain heating. At Warm Springs Bay, 75 km from the plate boundary, an anomalously high heat flow of 150 mW m−2 can most plausibly be ascribed to the thermal spring activity from which its name is derived. At Quartz Hill, 240 km landward of the plate boundary, a value of 115 mW m−2 might indicate a transition to a province of high heat flow resulting from late Tertiary and Quaternary extension and volcanism.

Petrology and provenance of pre–Late Devonian sandstones, Shoo Fly Complex, northern Sierra Nevada, California

Between Quartz Hill and Fall Creek Mountain, California, the Shoo Fly Complex includes the Poison Canyon and Red Hill formations. Field, biostratigraphic, and U-Pb zircon data indicate that both formations are most likely post-Cambrian and pre-Middle Devonian in age. Medium-grained and pebbly sandstone in both formations was deposited in submarine-fan environments by subaqueous sediment gravity flows laden with continentally derived detritus. The source of terrigenous detritus in the Poison Canyon and Red Hill formations included rocks that contained zircons as old as ∼2.09 b.y. The depositional basin in which the Poison Canyon and Red Hill formations accumulated was floored by oceanic lithosphere and was close enough to some continental landmass to have received sand-sized detritus derived from it. The continental landmass may have been located in western North America, but there is nothing in the data presented here that precludes the possibility that it was located on some foreign continent.

Timing of pre-Antler deformation in the Shoo Fly Complex, Sierra Nevada, California

The Shoo Fly Complex between Quartz Hill and Fall Creek Mountain contains Paleozoic folds and probable thrust faults that predate the intrusion of the Bowman Lake batholith. U-Pb analyses from six zircon fractions show that the youngest phase of the batholith is 409 ± 16 m.y. old. Previous suggestions that Paleozoic deformation in the Shoo Fly Complex is an early expression of the Late Devonian–Early Mississippian Antler orogeny are now viewed as less likely because the Antler orogeny postdated deformation of the Shoo Fly by at least 20 m.y.

Quartz Hill, Alaska: ABSTRACT

The Quartz Hill molybdenum deposit, located 44 mi (70 km) east of Ketchikan, Alaska, contains one of the world's largest concentrations of molybdenite. It is related to a Miocene intrusive complex referred to as the Quartz Hill stock. This deposit was discovered in 1974 by U.S. BORAX geologists as a result of a comprehensive reconnaissance geochemical rock and stream sediment sampling program designed to explore the western margin of the Coast Range batholithic complex on the mainland portion of southeastern Alaska. The country rocks of the area, orthogneisses and paragneisses, are intruded by the Quartz Hill stock which represents at least five phases of igneous activity. The main rock type within the Quartz Hill stock is a quartz monzonite which has been intruded by steeply dipping bodies of porphyritic quartz latite, and late quartz monzonite. These rocks are chemically and mineralogically similar and consist of quartz, K-feldspar, sodic plagioclase, and minor biotite, with many of the textures suggesting isothermal quench textures. These intrusive felsic rocks have been subsequently intruded by regional dikes of felsic and intermediate composition. The Quartz Hill orebody occurs entirely within the Quartz Hill composite stock. The orebody forms a large, tabular to slightly convex downward shape and is at or near the surface. Molybdenite is the only mineral of economic importance. The ore body is approximately 9,200 ft (2,800 m) long by 4,900 ft (1,500 m) wide and extends from the surface to a depth of 1,215 to 1,640 ft (370 to 500 m). Reserve calculations have projected approximately 2.5 billion tons grading 0.125% MoS2. End_of_Article - Last_Page 984------------

Petrology, composition, and age of intrusive rocks associated with the Quartz Hill molybdenite deposit, southeastern Alaska

A large porphyry molybdenum deposit (Quartz Hill deposit) was recently discovered in the heart of the Coast Range batholithic complex about 70 km east of Ketchikan, southeastern Alaska. Intrusive rocks associated with the mineral deposit form two composite epizonal to hypabyssal stocks and many dikes in country rocks. The stocks are characterized by a variety of textural rock types varying from equigranular or weakly seriate biotite granite to porphyries with aphanitic or very fine grained and aplitic groundmasses. These rocks contain about equal amounts of quartz, albitic plagioclase, and microperthitic microcline and less than 2.5% biotite. Unaltered rocks contain between 0.2 and 1% CaO, less than 1.7% combined Fe2O3, FeO, and MgO, and 74.4 to 77.7% SiO2. Total alkalis are between 8 and 9%, and K2O/Na2O is about 1.1. The range of major-oxide variation is small, but it is systematically related to lithology. Many trace-elements, including B, Pb, Sn, and Li have low concentrations. Intrusive rocks associated with the Quartz Hill deposit are more albitic and possibly trace-element depleted compared to some other rocks associated with porphyry molybdenum deposits.All observed metallization and alteration is within the Quartz Hill stock. Molybdenite forms fracture coatings and occurs in veins with quartz. Alteration is widespread and includes development of secondary quartz, pyrite, K-feldspar, biotite, white mica, chlorite, and zeolite. Field relations indicate that the stocks were emplaced after regional uplift and erosion of the Coast Range batholithic complex, and K–Ar data show that intrusion and alteration took place in late Oligocene time, about 27 to 30 Ma ago. Data from the Ketchikan quadrangle indicate that porphyry molybdenum metallization in the Coast Range batholithic complex is associated with regionally extensive but spotty, middle Tertiary or younger, felsic magmatism.

Pliocene and Quaternary geology of Mana Island (Note)

Abstract Mana Island, off the south-west coast of the North Island, is capped by the Mana Surface which dips south-east at about 2°. This dip is considered to be tectonic in origin. The surface, considered to be a marine abrasion platform, has no overlying deposits except late Quaternary loesses. No continuity with mainland surfaces can be demonstrated, but correlation with the Quartz Hill Surface, of probable early Pliocene age, is thought possible. Below the Mana Surface seven marine benches and gravel terraces have restricted distribution. Such benches and terraces are considered to have formed during successive interglacials. Terrestrial deposits include a deeply weathered post-Mana Surface fanglomerate and, in the east, a Holocene fluvial terrace.