Abstract The supergiant Grasberg porphyry deposit in Papua, Indonesia (5.26 Gt @ 0.61% Cu and 0.57 g/t Au, with no cutoff applied) is hosted by the Grasberg Igneous Complex that fills an upward-flared diatreme ~1,800 m wide at the 4,250-m surface elevation. The Grasberg Igneous Complex is emplaced into folded and strike-slip faulted Tertiary and older sediments and comprises 3.6 to 3.3 Ma Dalam monzodiorite intrusions and subordinate volcanic rocks occupying much of the pipe, the central 3.2 Ma Main Grasberg intrusion, and the NW-SE-trending 3.2 to 3.0 Ma Kali dikes. The Grasberg Igneous Complex contains two porphyry systems: Gajah Tidur copper-(molybdenum) and Main Grasberg copper-gold. The Gajah Tidur intrusion belongs to the Dalam igneous group and is a 3.4 Ma porphyritic monzonite with its top at a 2,750-m elevation; it is overprinted by an extensive, domal, quartz stockwork, with a low-grade and intensely phyllic-altered core, surrounded by molybdenite-bearing veins, with a pre-Main Grasberg Re-Os age, as well as chalcopyrite and overprinting pyrite-covellite veins. The strongly potassic-altered, Main Grasberg monzodiorite porphyry extends from surface to the 2,700-m elevation and is overprinted by a cylindrical, ~1-km-diameter, intense quartz-magnetite stockwork cut by abundant chalcopyrite-bornite veins with rare molybdenite dated at 3.09 Ma. A 700-m-wide annulus of chalcopyrite overprinted by pyrite-covellite-mineralized phyllic alteration surrounds the stockwork. Altered and mineralized Main Grasberg and surrounding Dalam rocks were subsequently wedged apart by the largely unmineralized Kali dikes. Gold is predominantly associated with the Main Grasberg porphyry system where it occurs as 1- to 150- µ m (avg ~15 µ m) native gold inclusions within chalcopyrite and bornite. Melt and fluid inclusions from Main Grasberg stockwork quartz veins, which exhibit crack-seal textures, comprise K-feldspar-rich silicate melt, sulfide melt, virtually water-free salt melt, and coexisting hypersaline and vapor-rich fluids. Factors important in forming the Grasberg deposit include the following: (1) generation of highly oxidized fertile magma in a postsubduction tectonic setting; (2) efficient extraction of metals from the parental magma chamber; (3) prolonged maintenance of a fluid-accumulating cupola in a strike-slip structural setting that delivered multiple overlapping discharges of metal-rich fluid; (4) highly focused fluid flow into a narrow, permeable stockwork zone in which a steep temperature gradient enabled highly efficient copper and gold precipitation and led to high ore grades; (5) limited dilution by postmineral intrusions; (6) the youthfulness of the deposit minimized erosion and resulted in preservation of nearly all the high-grade Main Grasberg porphyry orebody; and (7) the proximity of the two porphyry centers enables them to be mined as a single, large deposit. The Gajah Tidur copper-(molybdenum) and Main Grasberg copper-gold porphyry centers overlap in space and formed within ~250,000 years of one another. However, their distinct metal endowment, depth of emplacement, and geometry indicate that they formed under different magmatic, hydrothermal, and structural conditions, which are the subject of ongoing research.

Abstract In response to rising concerns about atmospheric carbon dioxide (CO 2 ) levels and likely regulations on emissions, investigations into geologic carbon storage options across the United States are underway. In the Midwest, Cambrian sandstones are major targets for potential geologic carbon storage. In some localities, the overlying Cambrian–Ordovician Knox Group is also being investigated as a possible target for primary and secondary storage of CO 2 . The thick dolomitic succession contains intervals that may function as both reservoirs and seals. Gas storage fields in Knox carbonates in Kentucky and Indiana demonstrate that methane can be safely stored in paleotopographic highs along the Knox unconformity surface. Numerous injection wells have also been completed in the Knox Group for brine disposal. More significantly, at least seven class 1 injection wells have used the Knox as all or part of a storage reservoir for industrial wastes. Many of these wells have injected millions of gallons of liquid waste annually into Knox reservoirs. The relative scale of these injection operations can be used to estimate the types and sizes of potential reservoirs within the Knox succession in the Midwest. Specific data on the Knox interval relative to its carbon storage and confining potential are currently being collected from wells drilled as part of U.S. Department of Energy administered carbon storage projects, as well as state-administered carbon storage programs. In this chapter, initial results of carbon storage tests are summarized from the Battelle 1 Duke Energy well, Kentucky Geological Survey 1 Blan well, Battelle-American Electric Power (AEP) 1 Mountaineer well, and Battelle-Ohio Geological Survey 1 CO 2 well. The AEP Mountaineer Power Plant will host the nation’s first commercially integrated carbon capture and geologic storage project, and the storage reservoirs will be in the Knox Group. Because the Knox Group is widespread at depth across much of the Midwest, it will be an important part of sequestration programs as confining interval and reservoir.

Abstract The Gulf Coast is a young basin with many geologic features that commonly are regarded as critical to the development of sediment-hosted mineral deposits. Metalliferous formation waters are locally present in the Gulf Coast Basin and have been proposed as modern analogs for the ore-forming fluids for ore deposits in older sedimentary terranes. Synsedimentary growth faults are important features that control local depositional facies and subsequent fluid movement in the Gulf Coast. Zn-Pb-Ag sulfide concentrations in salt dome cap rocks and shelf carbonates have been identified in the Gulf Coast. These sulfides have the most direct genetic affinity with Mississippi Valley type ore deposits that typically occur in older sedimentary terranes, although the cap rock occurrences have some similarities to SEDEX-style mineralization. Recently discovered barite mounds on the floor of the Gulf of Mexico provide a modern analog for the seafloor discharge of metal-bearing formation waters in a sedimentary basin. Salt dome cap rock mineralization is thought to be the result of the episodic injection of a deep-sourced, relatively hot, metal-bearing brine into the shallow cap rock environment where it mixed with a cool, dilute solution that was rich in H 2 S produced by bacterial sulfate reduction accompanying hydrocarbon oxidation. Reaction path geochemical modeling with SOLVEQ/CHILLER supports this model for the massive sulfide mineralization within the bioepigenetic calcite cap rocks and also shows that simple cooling (by 25 to 50°C) of a brine saturated with metal sulfides under reservoir conditions would lead to the precipitation of the sulfides. Adding H 2 S to a fluid close to saturation with respect to Fe, Zn, and Pb sulfides also would cause sulfide deposition without calcite deposition, as both the addition of H 2 S and sulfide deposition have the effect of lowering the pH, thus inhibiting calcite precipitation. This mechanism may explain the formation of the anhydrite-hosted stratiform sulfide laminae that formed at the salt/cap rock contact during the accretion of the anhydrite cap rock. Modeling further suggests that some H 2 S-rich brines (with low Zn and Pb contents) could contain appreciable dissolved Ag which would produce Ag-rich concentrations upon cooling or dilution. These geological and geochemical features support a genetic relationship among petroleum destruction, sulfate reduction by bacterial or thermochemical mechanisms, and Fe-Zn-Pb-Ag sulfide and Ba-Sr sulfate precipitation in environments ranging from ocean floor precipitates that are analogous to sedimentary exhalative ore deposits to deep intrastratal positions in carbonate formations that are similar to Mississippi Valley type deposits.

Abstract Salt domes, their cap rocks, and the adjacent sedimentary strata represent a major economic resource in the Gulf Coast and elsewhere. The resources and utilization of the salt dome setting are remarkably diverse. Major economic products of the salt dome environment are salt, cap rock-hosted native sulfur deposits, and oil and gas that occur on the dome flanks and in the cap rock. Some cap rocks are sources of limestone, gypsum, and anhydrite, and some host commercial concentrations of Zn and Pb. Uranium is concentrated in strata above or adjacent to some diapirs. Caverns, excavated within the salt, serve as product storage as diverse as crude oil, including the Strategic Petroleum Reserve, liquified petroleum gas, and hazardous waste. In addition, the Gulf Coast is a geologically young basin with many components that commonly are regarded as critical for the development of sediment-hosted mineral deposits. Metalliferous formation waters are locally present in the Gulf Coast Basin and have been proposed as modern analogs for the ore-forming fluids for ore deposits in older sedimentary terranes. Synsedimentary growth faults are important features that control local depositional facies and subsequent fluid movement in the Gulf Coast. Zn-Pb-Ag sulfide concentrations in two principal host settings (salt dome cap rocks and shelf carbonates) have been identified in the Gulf Coast. These sulfides have the most direct genetic affinity with Mississippi Valley type ore deposits that typically occur in older sedimentary terranes, although the cap rock occurrences have similarities to SEDEX-style mineralization. Recently discovered barite mounds on