Disseminated sulphide mineralisation at Garbh Achadh, Argyllshire, Scotland

A brief investigation of low-grade copper mineralisation associated with a small, talc-alkaline porphyry intrusion of Caledonian age is described. Geological mapping has delineated a small stock of biotite-feldspar 2 porphyry, 0.25 km in area, intruded into a sequence of Dalradian schists and quartzites with inter-bedded epidiorites. Disseminated sulphides occur within the porphyry and the hornfelsed epidiorite but do not normally , exceed 3% of the rock by volume. Assays of both rock types obtained maximum levels of 0.24% Cu. Hydrothermal alteration is prominent within the porphyry, with the widespread development of sericite and kaolinite. Subsequent faulting apparently exerted some control on the present limits of alteration and mineralisation. Several small strata-bound lenses of massive sulphide within the metasediments were recorded but were not investigated in detail. Geochemical rock-sampling delineated a strong arcuate copper anomaly over the northern epidiorite/porphyry contact and a more subdued anomaly along the southern faulted contact. Molybdenum shows a similar distribution but is more closely confined to the porphyry. Overburden sampling demonstrated that little or no metal dispersion occurred within the overlying till, and stream sediment sampling of the catchment area showed that concentrations of copper decrease to background levels within 1 km of the intrusion. 1 Induced polarisation (IP) surveys produced a clearly defined grouping of chargeability anomalies around the edges of the porphyry stock but these showed no increase in magnitude at depth. Above background chargeability values recorded over the centre of the intrusion increase markedly towards the margins , possibly reflecting a pyritic halo. Most resistivity 'lows' coincide with fault zones and the results of a total intensity magnetometer 1 survey showed that, while most magnetic anomalies occur over epidiorites, I significant anomalies are also produced in the vicinity of fault zones. The results of the geological, petrographic, geochemical and I geophysical studies demonstrate the presence of several features : characteristic of 'porphyry copper style' mineralisation but the small 1 surface area and low grade of the deposit, combined with a lack of encouraging geophysical responses at depth, suggest that there is little II chance of discovering an economic orebody by exploratory drilling

The position of graptolites within Lower Palaeozoic planktic ecosystems.

An integrated approach has been used to assess the palaeoecology of graptolites both as a discrete group and also as a part of the biota present within Ordovician and Silurian planktic realms. Study of the functional morphology of graptolites and comparisons with recent ecological analogues demonstrates that graptolites most probably filled a variety of niches as primary consumers, with modes of life related to the colony morphotype. Graptolite coloniality was extremely ordered, lacking any close morphological analogues in Recent faunas. To obtain maximum functional efficiency, graptolites would have needed varying degrees of coordinated automobility. A change in lifestyle related to ontogenetic changes was prevalent within many graptolite groups. Differing lifestyle was reflected by differing reproductive strategies, with synrhabdosomes most likely being a method for rapid asexual reproduction. Direct evidence in the form of graptolithophage 'coprolitic' bodies, as well as indirect evidence in the form of probable defensive adaptations, indicate that graptolites comprised a food item for a variety of predators. Graptolites were also hosts to a variety of parasitic organisms and provided an important nutrient source for scavenging organisms

A new, morphologically diverse Permian trilobite fauna from Oman

A newly discovered trilobite fauna from the early to middle Permian Qarari Unit of northeastern Sultanate of Oman is described. It comprises exceptionally complete and well-preserved examples of five proetoid species, belonging to genera typical of an eastern Tethyan region extending through southern Asia to Timor. The shallow shelf fauna compares closely with one of Artinskian age from Afghanistan. Permian species previously assigned to Paladin are here considered unrelated to this predominantly Carboniferous clade, and are placed in a new ditomopygine genus, Simulopaladin, type species Simulopaladin tridentifer sp. nov. Three other ditomopygine species are described: Hentigia ornata sp. nov., Iranaspidion elephas sp. nov., and Acanthophillipsia felicitae sp. nov. The proetid Triproetus bonbon sp. nov. is the most complete material known of a more widespread genus

Devonian trilobites at Buill, Chile (42°S)

Trilobites devonicos de Buill, Chile (42°S). Se describe un trilobites calmoniido (Calmoniidae gen. nov. aff. Bainella Rennie, 1930) un trilobites lacopoide indeterminado y un coral zafrentido, recolectados en rodados de pizarras en Buill, Chile (42°24'S; 72°43'W), en los Andes de Chiloe. Esta faunula es consistente con una edad de sedimentacion devonica interior, para al menos parte del complejo acrecionario del sur de Chile, que aflora extensamente al oeste de Buill y que fue metamorfizado en el Paleozoico Superior a Mesozoico inferior. La presencia de una asociacion faunistica de Gondwana meridional, que puede ser comparada con faunas devonicas de Argentina, Bolivia, Islas Malvinas (Falkland) y Sudafrica, sugiere que esta area formaba parte de una extensa plataforma somera durante el Devonico

Trilobite spines and beetle horns: sexual selection in the Palaeozoic?

Raphiophorid trilobites commonly bore median cephalic protuberances such as spines or bulbs, showing a remarkable variety of form. It is unlikely that their primary function was for protection or in hydrodynamics. A case is made that they were secondary sexual features, by comparison with similar morphological structures developed on rhinoceros beetles and other arthropods. This interpretation is supported by four lines of evidence: their ontogeny, their diversity, the existence of plausible examples of sexual dimorphs in some cases and the fact that they show positive allometry