Geochemical evidence for magmatic fluids in porphyry copper mineralization

The Koloula Igneous Complex comprises 26 different intrusive phases that have been divided into two major magmatic episodes — cycle 1 intrusions (4.5 Ma) and cycle 2 intrusions (2.4 to 1.5 Ma). The cycle 2 intrusions are further divided into the Inamumu Zoned Pluton (IZP) which is composed of 6 concentrically disposed quartz diorite and tonalite units; and several satellite intrusions. The IZP is host to porphyry-copper mineralization, whereas the cycle 1, and cycle 2 satellite intrusions are barren. Presently exposed mineralization in the IZP (A system) represents the deeply eroded core of a porphyry copper system, where widely-spaced veinlet alteration envelopes ( 1 mm thick) are separated by large volumes of unaltered rock.Compositional trends in biotites and amphiboles from both individual grains and throughout the differentiation series of the IZP, indicate fluctuating but generally increasing existed through the sequence from early magmatic late magmatic early hydrothermal conditions. In amphiboles, compositional domains (Mg-rich) that are indicative of high are correlated with episodes of fluid exsolution, independent evidence of which is provided by multiple generations of fluid inclusions in quartz phenocrysts. These high domains in amphiboles have higher Si, Mn, and Ca contents, but are depleted in Fe, Ti, Na, K, and Cl relative to the less oxidizing domains. The latter elements are those that are known from veinlet alteration assemblages and fluid-inclusion evidence to have been preferentially partitioned into the co-existing fluid phase (late magmatic hydrothermal solution).By contrast, amphiboles from barren rock types that are slightly older than, and of the same age as the IZP, exhibit restricted compositional ranges, and are more Fe-rich. Some individual grains and two cycle 2 satellite intrusions indicate Fe-enrichment during progressive crystallization. Siliceous deuteric amphiboles are commonly as Mg-rich as the high amphibole domains from the IZP, but are easily distinguished from them by their lack of smooth compositional trends versus Si, and by their highly variable Mg and Fe contents.Biotites from the IZP also indicate progressive oxidation, whereas biotites from the barren rock types show either little compositional variation or progressive Fe-enrichment. Biotites from the barren intrusions are richer in Cl, Li and Rb and poorer in Ba than those of the mineralizing intrusions. fHF was very low ( 0.003 bars) in both barren and mineralizing intrusions. During progressive differentiation, Rb content decreased and Ba content increased in IZP biotites, which is atypical, yet explicable owing to the former presence of a competing fluid phase during biotite crystallization.Because is a function of degree of fluid exsolution, then in igneous systems with sufficient Cu, Cl, and ultimately S, progressively higher should potentially lead to more mineralized intrusions. Higher is reflected by steeper Fe versus Si gradients in amphibole domains. Indeed, such a graph for amphiboles from 5 igneous complexes, indicates that two economically mineralized units produced steeper FeSi than those from weakly mineralized intrusions. Steep FeSi trends that do not continue to amphibole domains more siliceous than Si=7.3 (atoms per 23 oxygens) are unlikely to have resulted from subsolidus crystallization and these intrusions are unlikely to be strongly mineralized.     

Movements of spawning rainbow smelt,Osmerus mordax,in a massachusetts estuary

Movements of spawning rainbow smelt, Osmerus mordax, were followed in the Parker River estuary, Massachusetts during 1974 and 1975. Fish marked with vinyl subcutaneous tags (n=1,492) or fin clips (n=577) were recaptured on three separate spawning sites in three different tributaries; the distribution patterns of marked fish indicated a homogeneous spawning stock. Interstream movement may have been facilitated by tidal transport since smelt ascended to the spawning sites on flood tides and moved downstream as tides ebbed. Rates of recapture of fish tagged on the spawning areas were 2.61 and 5.61 times greater for males than females in 1974 and 1975 respectively. Individual tagged males were recovered up to four times during the spawning period; females were recaptured a maximum of once. The proportion of age II and older females sampled from the angling fishery prior to spawning in 1975 (47.38%) was greater than the cumulative proportion sampled on the spawning sites (11.93%) due to longer spawning period of individual males.     

Vibration tests on emosson arch dam,Switzerland

Measurements have been made of vibrations induced in the 180 m high Emosson arch dam in Switzerland³ by a system of mechanical eccentric-mass vibrators and by the natural wind. Details are given of the dam itself, the tests and the experimental results obtained. Finite element calculations made before the tests, which include reservoir and foundation effects, are compared with the measurements.     

196Hg and202Hg isotopic ratios in chondrites: revisited

Additional evidence for an isotopically anomalous Hg fraction in unequilibrated meteorites has been obtained using neutron activation to produce¹⁹⁶Hg and²⁰²Hg followed by stepwise heating to extract the Hg. In the latest experiments Allende matrix samples released the anomalous Hg but various high-temperature inclusions did not. Nucleogenetic processes are suggested as the probable cause of the anomaly.     

The halogens in Luna 16 and Luna 20 soils

Cl and P₂U₅ do not appear to exhibit the same correlation in soils from the Luna 20 and possibly the Luna 16 sites as they do in samples from the Apollo 11–15 sites. Nevertheless, the coherence between labile Cl and other KREEP-related elements is maintained.     

Compositions of magmatic hydrothermal fluids determined by LA-ICP-MS of fluid inclusions from the porphyry copper–molybdenum deposit at Butte, MT

We analyzed 85 fluid inclusions from seven samples from the porphyry Cu–Mo deposit in Butte, MT, using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). The Butte deposit formed at unusually great depth relative to most porphyry deposits, and fluid inclusions in deep veins trapped a low-salinity, CO₂-bearing, magmatically derived, supercritical fluid as a single aqueous phase. This fluid is interpreted to be the parent fluid that cooled, decompressed, unmixed, and reacted with wall rock to form the gigantic porphyry Cu deposit at Butte. Few previous analyses of such fluids exist.Low-salinity, aqueous fluids from the earliest veins at Butte are trapped in deep veins with biotite-rich alteration envelopes (EDM veins). These veins, and the Butte quartz monzonite surrounding them, host much of the Butte porphyry Cu mineralization. Twenty fluid inclusions in one EDM quartz vein are dominated by Na, K, Fe (from 0.1 to 1 wt.%) and contain up to 1.3 wt.% Cu. These inclusions contain only small amounts (tens of ppm) of Pb, Zn, and Mn, and typically contain Li, B, Ca, As, Mo, Ag, Sn, Sb, Ba, and W in less than detectable quantities. The abundance of Cu in early fluids indicates that a low-salinity, Cu-rich, aqueous ore fluid can be directly produced by aqueous fluid separation from a granitic magma. Similar inclusions (eight) in an early deep quartz–molybdenite vein with a K-feldspar selvage have similar compositions but contain significantly less Cu than most inclusions in the biotite-altered vein. Analyzed inclusions in both veins contain less than detectable concentrations of Mo even though one is molybdenite-bearing.Low-salinity, CO₂-bearing aqueous fluids are also trapped in pyrite–quartz veins with sericitic selvages. These veins cut both of the above vein types and contain inclusions that were trapped at lower pressure and temperature. Thirty-nine inclusions in two such veins have compositions similar to early fluids, but are enriched by up to a factor of 10 in Mn, Pb, and Zn relative to early fluids, and are slightly depleted in Fe. Many of these inclusions contain as much or more Cu than early fluids, although little chalcopyrite is found in or around pyrite–quartz veins.Eighteen halite-bearing inclusions from three veins from both chalcopyrite-bearing and barren veins with both K-silicate and sericitic selvages were analyzed as well. Halite-saturated inclusions are dominated by Na, K, Fe, and in some inclusions Ca. Whereas these inclusions are significantly enriched in Ca, Mn, Fe, Zn, and Pb, fluids in all three veins contain significantly less Cu than early, high temperature, low-salinity inclusions.Analyses of all inclusion types show that whereas bulk-salinity of the hydrothermal fluid must be largely controlled by the magma, fluid–rock interactions have a significant role in controlling fluid compositions and metal ratios. Cu concentrations range over an order of magnitude, more than any other element, in all four samples containing low-salinity inclusions. We infer that variations are the result of fluid trapping after different amounts of fluid–rock reaction and chalcopyrite precipitation. Enrichment, relative to early fluids, of Mn, Pb, and Zn in fluids related to sericitic alteration is also likely the result of fluid–rock reaction, whereby these elements are released from biotite and feldspars as they alter to sericite. In halite-bearing inclusions, concentrations of Sr, Ca, Pb, and Ba are elevated in inclusions from the pyrite–quartz vein with sericitic alteration relative to halite-bearing inclusions from unaltered and potassically altered samples. Such enrichment is likely caused by the breakdown of plagioclase and K-feldspar in the alteration envelope, releasing Sr, Ca, Pb, and Ba.     

Clutch, egg and body size variation among common eiders breeding in Hudson Bay, Canada

The Hudson Bay common eider ( Somateria molissima sedentaria ) is a unique subspecies of eider that remains within the confines of Hudson Bay throughout the year. We compared clutch, egg and body size variation among populations of common eiders breeding in eastern and western Hudson Bay. Clutch size did not differ substantially among these populations. All eiders in Hudson Bay laid larger clutches than other subspecies in eastern North America. As Hudson Bay common eiders do not undergo extensive migrations, they may have more energy reserves available to them for egg production. Eiders nesting in eastern Hudson Bay laid larger eggs than eiders nesting in western Hudson Bay. Further, eiders in eastern Hudson Bay tended to be structurally larger, but had smaller bill processes. These differences may have a genetic basis. Smaller egg size and body size may arise in western Hudson Bay from mixing with the smaller borealis subspecies nesting to the north. Further work to resolve genetic affinities, determine levels of male and female dispersal, and examine variation in reproductive ecology are needed to resolve the sources of these differences.