David R. Cooke

Bio: David R. Cooke is an academic researcher from University of Tasmania. The author has contributed to research in topics: Porphyry copper deposit & Volcanic rock. The author has an hindex of 50, co-authored 192 publications receiving 8890 citations. Previous affiliations of David R. Cooke include University College London & York University.

Giant Porphyry Deposits: Characteristics, Distribution, and Tectonic Controls

Abstract: More than half of the 25 largest known porphyry copper deposits, defined in terms of contained copper metal, formed during three time periods: the Paleocene to Eocene, Eocene to Oligocene, and middle Miocene to Pliocene. These giant deposits are clustered within three provinces, central Chile, northern Chile, and southwest Arizona-northern Mexico. Other giant deposits occur in Montana, Utah, Panama, Peru, Argentina, Irian Jaya, Mongolia, and Iran. Compressive tectonic environments, thickened continental crust, and active uplift and erosion were associated with the formation of many of these deposits. Calc-alkalic magmas are most favorable for the formation of giant porphyry copper deposits, although several of the largest systems are associated with high K calc-alkalic intrusions. The 25 largest gold-rich porphyry deposits are concentrated in the southwest Pacific and South America, with other occurrences in Eurasia, British Columbia, Alaska, and New South Wales. Many of the deposits formed in the last 13 m.y. The largest of the deposits are associated with high K calc-alkalic intrusions. Many calc-alkalic porphyritic intrusions have also produced giant gold-rich porphyries. In the last 20 m.y., the formation of giant porphyry copper-molybdenum and copper-gold deposits in the circum-Pacific region has been closely associated with subduction of aseismic ridges, seamount chains, and oceanic plateaus beneath oceanic island and continental arcs. In several examples, these tectonic perturbations have promoted flat-slab subduction, crustal thickening, uplift and erosion, and adakitic magmatism coeval with the formation of well-endowed porphyry and/or epithermal mineral provinces. Similar tectonic features are inferred to be associated with the giant porphyry copper-molybdenum provinces of northern Chile (Eocene-Oligocene) and southwest United States (Cretaceous-Paleocene). Topographic and thermal anomalies on the downgoing slab appear to act as tectonic triggers for porphyry ore formation. Other factors, such as sutures in the overriding plate, permeability architecture of the upper crust, efficient processes of ore transport and deposition, and, in some cases, formation and preservation of supergene enrichment blankets are also vital for the development of high-grade giant ore deposits. A low-grade geochemical anomaly may be the final product of mineralization, if ore-forming processes do not operate efficiently, even in the most favorable geodynamic settings.

US Cosmic Visions: New Ideas in Dark Matter 2017: Community Report

Abstract: This white paper summarizes the workshop "U.S. Cosmic Visions: New Ideas in Dark Matter" held at University of Maryland on March 23-25, 2017.

Trace elements in sulfide minerals from eastern Australian volcanic-hosted massive sulfide deposits; Part I, Proton microprobe analyses of pyrite, chalcopyrite, and sphalerite, and Part II, Selenium levels in pyrite; comparison with delta 34 S values and implications for the source of sulfur in volcanogenic hydrothermal systems

Abstract: Part I Pyrite, chalcopyrite, and sphalerite from six volcanic-hosted massive sulfide (Mount Chalmers, Rosebery, Waterloo, Agincourt, Dry River South, and Balcooma) deposits in eastern Australia were analyzed using a proton microprobe to determine trace element abundances In pyrite, trace elements can be divided into three groups according to the most likely occurrence of the element: (1) elements that occur mainly as inclusions (Cu, Zn, Pb, Ba, Bi, Ag, and Sb), (2) elements that occur as nonstoichiometric substitutions in the lattice (As, Tl, Au, and possibly Mo), and (3) elements that occur as stoichiometric substitutions for Fe (Co and Ni) or S (Se and Te) Hydrothermal and metamorphic recrystallization cleans pyrite of group 1 and group 2 elements, but does not appear to affect the concentrations of group 3 elements Colloform pyrite grains have the highest levels of As and Au (up to 200 ppm), suggesting that rapid precipitation is important in incorporating Au into auriferous pyrite Elements that occur as inclusions in chalcopyrite include Pb, Bi, Zn (P), and Ba The occurrence of As and Sb is unresolved, although consistently high values of As in some samples suggest that As may substitute into the lattice of chalcopyrite Elements that substitute into the lattice include Ag (for Cu), In, Sn and Zn (?) (for Fe), and Se (for S) Lead, Ba, Sb, possibly, and in some cases, Cu, occur commonly as inclusions in sphalerite Lattice substitutions in sphalerite include Fe, Cd, Cu (to 4,500 ppm), Ni, In, Ag, Te, Ga and possibly Mo In addition, consistently high (2,000-4,000 ppm) levels of As in the Rosebery barite zone may indicate As lattice substitution Part II The Se content of pyrite in volcanic-hosted massive sulfide deposits varies as follows: in Cu-poor, Zn-rich deposits, Se levels are low (mainly <5 ppm) throughout; in Cu-rich deposits, Se levels are highest (10-200 ppm) in stringer zones and the lower part of the massive sulfide lens, and decrease toward the top of the massive sulfide lens and into peripheral altered rocks Metamorphic recrystallization does not affect these variations Although delta 34 S values also vary systematically in individual deposits, no systematic differences were noted between Cu-rich and Zn-rich deposits

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Short-Chain Fatty Acids and Human Colonic Function: Roles of Resistant Starch and Nonstarch Polysaccharides

Abstract: Resistant starch (RS) is starch and products of its small intestinal digestion that enter the large bowel. It occurs for various reasons including chemical structure, cooking of food, chemical modification, and food mastication. Human colonic bacteria ferment RS and nonstarch polysaccharides (NSP; major components of dietary fiber) to short-chain fatty acids (SCFA), mainly acetate, propionate, and butyrate. SCFA stimulate colonic blood flow and fluid and electrolyte uptake. Butyrate is a preferred substrate for colonocytes and appears to promote a normal phenotype in these cells. Fermentation of some RS types favors butyrate production. Measurement of colonic fermentation in humans is difficult, and indirect measures (e.g., fecal samples) or animal models have been used. Of the latter, rodents appear to be of limited value, and pigs or dogs are preferable. RS is less effective than NSP in stool bulking, but epidemiological data suggest that it is more protective against colorectal cancer, possibly via butyrate. RS is a prebiotic, but knowledge of its other interactions with the microflora is limited. The contribution of RS to fermentation and colonic physiology seems to be greater than that of NSP. However, the lack of a generally accepted analytical procedure that accommodates the major influences on RS means this is yet to be established.

Handbook of Chemistry and Physics

Abstract: There is a special reason for reviewing this book at this time: it is the 50th edition of a compendium that is known and used frequently in most chemical and physical laboratories in many parts of the world. Surely, a publication that has been published for 56 years, withstanding the vagaries of science in this century, must have had something to offer. There is another reason: while the book is a standard fixture in most chemical and physical laboratories, including those in medical centers, it is not as frequently seen in the laboratories of physician's offices (those either in solo or group practice). I believe that the Handbook can be useful in those laboratories. One of the reasons, among others, is that the various basic items of information it offers may be helpful in new tests, either physical or chemical, which are continuously being published. The basic information may relate

Porphyry Copper Systems

Abstract: Porphyry Cu systems host some of the most widely distributed mineralization types at convergent plate boundaries, including porphyry deposits centered on intrusions; skarn, carbonate-replacement, and sediment-hosted Au deposits in increasingly peripheral locations; and superjacent high- and intermediate-sulfidation epithermal deposits. The systems commonly define linear belts, some many hundreds of kilometers long, as well as occurring less commonly in apparent isolation. The systems are closely related to underlying composite plutons, at paleodepths of 5 to 15 km, which represent the supply chambers for the magmas and fluids that formed the vertically elongate (>3 km) stocks or dike swarms and associated mineralization. The plutons may erupt volcanic rocks, but generally prior to initiation of the systems. Commonly, several discrete stocks are emplaced in and above the pluton roof zones, resulting in either clusters or structurally controlled alignments of porphyry Cu systems. The rheology and composition of the host rocks may strongly influence the size, grade, and type of mineralization generated in porphyry Cu systems. Individual systems have life spans of ~100,000 to several million years, whereas deposit clusters or alignments as well as entire belts may remain active for 10 m.y. or longer. The alteration and mineralization in porphyry Cu systems, occupying many cubic kilometers of rock, are zoned outward from the stocks or dike swarms, which typically comprise several generations of intermediate to felsic porphyry intrusions. Porphyry Cu ± Au ± Mo deposits are centered on the intrusions, whereas carbonate wall rocks commonly host proximal Cu-Au skarns, less common distal Zn-Pb and/or Au skarns, and, beyond the skarn front, carbonate-replacement Cu and/or Zn-Pb-Ag ± Au deposits, and/or sediment-hosted (distal-disseminated) Au deposits. Peripheral mineralization is less conspicuous in noncarbonate wall rocks but may include base metal- or Au-bearing veins and mantos. High-sulfidation epithermal deposits may occur in lithocaps above porphyry Cu deposits, where massive sulfide lodes tend to develop in deeper feeder structures and Au ± Ag-rich, disseminated deposits within the uppermost 500 m or so. Less commonly, intermediate-sulfidation epithermal mineralization, chiefly veins, may develop on the peripheries of the lithocaps. The alteration-mineralization in the porphyry Cu deposits is zoned upward from barren, early sodic-calcic through potentially ore-grade potassic, chlorite-sericite, and sericitic, to advanced argillic, the last of these constituting the lithocaps, which may attain >1 km in thickness if unaffected by significant erosion. Low sulfidation-state chalcopyrite ± bornite assemblages are characteristic of potassic zones, whereas higher sulfidation-state sulfides are generated progressively upward in concert with temperature decline and the concomitant greater degrees of hydrolytic alteration, culminating in pyrite ± enargite ± covellite in the shallow parts of the litho-caps. The porphyry Cu mineralization occurs in a distinctive sequence of quartz-bearing veinlets as well as in disseminated form in the altered rock between them. Magmatic-hydrothermal breccias may form during porphyry intrusion, with some of them containing high-grade mineralization because of their intrinsic permeability. In contrast, most phreatomagmatic breccias, constituting maar-diatreme systems, are poorly mineralized at both the porphyry Cu and lithocap levels, mainly because many of them formed late in the evolution of systems. Porphyry Cu systems are initiated by injection of oxidized magma saturated with S- and metal-rich, aqueous fluids from cupolas on the tops of the subjacent parental plutons. The sequence of alteration-mineralization events charted above is principally a consequence of progressive rock and fluid cooling, from >700° to <250°C, caused by solidification of the underlying parental plutons and downward propagation of the lithostatic-hydrostatic transition. Once the plutonic magmas stagnate, the high-temperature, generally two-phase hyper-saline liquid and vapor responsible for the potassic alteration and contained mineralization at depth and early overlying advanced argillic alteration, respectively, gives way, at <350°C, to a single-phase, low- to moderate-salinity liquid that causes the sericite-chlorite and sericitic alteration and associated mineralization. This same liquid also causes mineralization of the peripheral parts of systems, including the overlying lithocaps. The progressive thermal decline of the systems combined with synmineral paleosurface degradation results in the characteristic overprinting (telescoping) and partial to total reconstitution of older by younger alteration-mineralization types. Meteoric water is not required for formation of this alteration-mineralization sequence although its late ingress is commonplace. Many features of porphyry Cu systems at all scales need to be taken into account during planning and execution of base and precious metal exploration programs in magmatic arc settings. At the regional and district scales, the occurrence of many deposits in belts, within which clusters and alignments are prominent, is a powerful exploration concept once one or more systems are known. At the deposit scale, particularly in the porphyry Cu environment, early-formed features commonly, but by no means always, give rise to the best ore-bodies. Late-stage alteration overprints may cause partial depletion or complete removal of Cu and Au, but metal concentration may also result. Recognition of single ore deposit types, whether economic or not, in porphyry Cu systems may be directly employed in combination with alteration and metal zoning concepts to search for other related deposit types, although not all those permitted by the model are likely to be present in most systems. Erosion level is a cogent control on the deposit types that may be preserved and, by the same token, on those that may be anticipated at depth. The most distal deposit types at all levels of the systems tend to be visually the most subtle, which may result in their being missed due to overshadowing by more prominent alteration-mineralization.