Influence of nearshore sediment dynamics on the distribution of heavy mineral placer deposits in Sri Lanka

Beach sediments in Sri Lanka contain industrial-grade heavy mineral occurrences. Samples of both offshore and onshore sediments were collected to examine the provenance, mineralogy and geochemical compositions of the heavy mineral occurrences. Coastal morphodynamic changes along the coastline of Sri Lanka were analyzed using the time-series satellite images. These coastal morphodynamic changes were used to identify the prominent directions of monsoon-influenced longshore currents, coastal sediment accretion and depositional trends and their relationships to the provenance of the heavy minerals. Results show the concentrations of detrital ilmenite, zircon, garnet, monazite, and rutile vary in the onshore and offshore sediments. The heavy mineral potential of the northeastern coast is high (average contents of about 45–50% in the Verugal deposit, 70–85% in the Pulmoddai deposit, and 3.5–5.0% in offshore samples stretching from Nilaveli to Kokkilai), compared to sediments in southwest (average content about 10% in onshore sediments and 2% in offshore sediments from the mouth of the Gin River). Therefore, no economic-grade heavy mineral placers were identified in the offshore environments. The high concentrations of heavy minerals in beach sediments and low concentrations in offshore sediments suggest operation of a panning system in the surf zone to form enriched placer deposits. Major and trace element compositions of beach sediments show marked enrichments of TiO₂, Fe₂O₃, La, Ce, Zr, Cr, Nb, Th and V compared to average Upper Continental Crust (UCC) values. Analysis of prominent coastal longshore transport patterns identifies bidirectional sediment transport in the northeast coast of Sri Lanka. In the southwestern coast, two transport directions occur with anti-clockwise transport from Galle to Hambantota, and clockwise transport from Hikkaduwa to Wadduwa. The heavy minerals in the placers were mainly derived from Precambrian metamorphic rocks, and transported to the coast through the river systems of Sri Lanka.     

The Stream Sediment Geochemistry of the Walawe Ganga Basin of Sri Lanka - Implications for Gondwana Mineralization

A regional geochemical and mineralogical study aimed at investigating the mineralization in the western-part of the Walawe Ganga (river) Basin in Sri Lanka is represented in this paper. The river basin is the 3^rd largest in the country and has within it a boundary zone between two geologically different crustal blocks, which are marked by granulitic grade rocks and amphibolite grade rocks. Size fractions of stream sediments (< 63 μm; 63–125 μm; 125–177 μm and 177–250 μm) developed on the granulite-grade metamorphic terrain have been analysed at their source for their mineralogical and selected element compositions. Thirty-eight (38) sediment samples and 15 representative probable parent rock samples were chemically analysed giving special emphasis to the High Field Strength trace Elements (HFSE) including the Rare Earth Elements (REE). The granulite grade rocks in the study area is geochemically similar to that of post Archean upper crust. However the stream sediments developed from the high-grade rocks during the intense weathering, are markedly enriched with HFSE and REE. The enrichment of HFSE and LREE is accounted for by the presence of HFSE- and REE- rich accessory mineral phases such as zircon, monazite, apatite, garnet and rutile in the sediments. In some samples, the content of heavy minerals contributes as much as 50 wt. %. These minerals act as a source of elements in the sediments. However, extreme hydraulic sorting of HFSE- and REE-bearing minerals during the sediment deposition cannot be expected within a short distance from near the sources except from a mineralized occurrence. Therefore, the higher enrichment of these elements presumably indicates occurrences of scattered mineral sources such as highly differentiated granites and associated pegmatites within the Walawe Ganga drainage basin. These granitic pegmatites are probably intruded during or soon after the main granulite-facies metamorphic event and similar events are seen in other terrains of East-Gondwana.     

Middle Pleistocene to Holocene activity of the Gondola Fault Zone (Southern Adriatic Foreland): Deformation of a regional shear zone and seismotectonic implications

Recent seismicity in and around the Gargano Promontory, an uplifted portion of the Southern Adriatic Foreland domain, indicates active E–W strike-slip faulting in a region that has also been struck by large historical earthquakes, particularly along the Mattinata Fault. Seismic profiles published in the past two decades show that the pattern of tectonic deformation along the E–W-trending segment of the Gondola Fault Zone, the offshore counterpart of the Mattinata Fault, is strikingly similar to that observed onshore during the Eocene–Pliocene interval. Based on the lack of instrumental seismicity in the south Adriatic offshore, however, and on standard seismic reflection data showing an undisturbed Quaternary succession above the Gondola Fault Zone, this fault zone has been interpreted as essentially inactive since the Pliocene. Nevertheless, many investigators emphasised the genetic relationships and physical continuity between the Mattinata Fault, a positively active tectonic feature, and the Gondola Fault Zone. The seismotectonic potential of the system formed by these two faults has never been investigated in detail. Recent investigations of Quaternary sedimentary successions on the Adriatic shelf, by means of very high-resolution seismic–stratigraphic data, have led to the identification of fold growth and fault propagation in Middle–Upper Pleistocene and Holocene units. The inferred pattern of gentle folding and shallow faulting indicates that sediments deposited during the past ca. 450 ka were recurrently deformed along the E–W branch of the Gondola Fault Zone.We performed a detailed reconstruction and kinematic interpretation of the most recent deformation observed along the Gondola Fault Zone and interpret it in the broader context of the seismotectonic setting of the Southern Apennines-foreland region. We hypothesise that the entire 180 km-long Molise–Gondola Shear Zone is presently active and speculate that also its offshore portion, the Gondola Fault Zone, has a seismogenic behaviour.     

Dahab stream sediments, southeastern Sinai, Egypt: a potential source of gold, magnetite and zircon

The stream sediments of Dahab area, southeastern Sinai, Egypt, were studied for their content of economic minerals. These sediments are immature as indicated by poor sorting and other mechanical parameters. They are derived from Precambrian basement rocks, which are mostly represented by granitic rocks in addition to lesser amounts of volcanics and gabbros. The mineralogical investigation revealed that these sediments contain considerable amounts of placer gold, Fe–Ti oxides and zircon.The concentrated Fe–Ti oxides comprise homogeneous magnetite and ilmenite in addition to ilmeno-magnetite, hemo-ilmenite and rutile–hematite intergrowths. Isodynamic separation of some raw samples of SIZE=1 mm revealed that up to 15.12% magnetic minerals can be recovered. Zircon shows remarkable variations in morphology, colour, chemistry and provenance. U-poor and U-rich varieties of zircon were discriminated containing UO₂ in the ranges of 0.04–1.19 and 3.05–3.68 wt.%, respectively. REE-bearing minerals comprise monazite, allanite and La-cerianite.On mineralogical basis, the present work suggests that Dahab stream sediments represent a promising target for further geochemical exploration for precious metals, especially gold. Fire assay data indicate that placer gold in the studied sediments sometimes reaches 15.34 g/t. Narrow gullies and valleys cutting the basement manifest the development and preservation of gold in this arid environment. Background concentration of gold and variation in lithology suggest multiple source of the metal in the investigated sediments.     

Ca distribution between almandine-rich garnet and plagioclase in pelitic and psammitic schists from the metamorphic basement of North-Eastern Sardinia

Garnet and plagioclase pairs from fourteen selected samples, from garnet to sillimanite zones, collected along a NS traverse throughout the metamorphic basement of NE Sardinia, have been analyzed by microprobe.Beyond the garnet isograd, plagioclase has albitic composition and the garnet (a Ca-rich almandine) shows Ca/ Ca+Mg+Fe ratios of about 0.35–0.30, fairly constant from core to rim.Towards the North, still in the garnet zone, when on the large albitic core of plagioclase a thin and discontinuous oligoclasic rim (An₂₂–An₁₈) formed, we observe in the garnet edge an abrupt decrease of the Ca/Ca+Mg+Fe ratio (0.27–0.16).In the staurolite and sillimanite zones garnet does not show significant Ca-zoning and it is characterized by low Ca content (Ca/Ca+Mg+Fe<0.1); the coexisting plagioclase has oligoclasic (An₁₆–An₂₇) composition.The chemical data and the microstructural evidence on growth time indicate that the garnet and plagioclase had a strong mutual interference in determining the relative Ca distribution.The most relevant reactions are discussed and, in particular, the antipathetical Ca-zoning, recorded by garnet and plagioclase in the garnet zone, is considered as the evidence of temperature increase during growth of the two minerals. It is also suggested that the sharp variation of Ca content at the garnet edge was controlled by the discontinuous nature of plagioclase solid solution in the peristeritic range.The order of appearance of garnet and oligoclase in the basement of NE Sardinia is also discussed in comparison with other well known metamorphic sequence (Vermont, New Zealand and Dalradian). It is concluded that the different order of appearance is controlled other than the different nature of the calcic phases in the lower grade zones also by the in the fluid phase.     

FEG-EPMA mapping and Fe-Ti oxide mineral chemistry of Brahmaputra River sediments in Bangladesh: provenance and petrogenetic implications

The present research deals with the FEG-EPMA mapping and Fe-Ti oxide mineral chemistry of Brahmaputra River sediments in Bangladesh. Major heavy minerals in the sediments consist of garnet (8.5–21.3%), kyanite (5.35–11.9%), monazite (2.3–5.3%), sillimanite (1.8–4.7%), zircon (3.6–9.1%), and a considerable amount of opaques mainly Fe-Ti oxide minerals (23.1–35.4%). The detrital Fe-Ti oxide minerals carry significant clues to the parent rocks or sources. In these contexts, detrital opaques (Fe-Ti oxides) have been analyzed with an electron probe microanalyzer (EPMA). These opaques (Fe-Ti oxide) display six types of textural patterns, dominantly seriate with granular, emulsion, and acicular sandwich structures and trellis type of textural patterns. These textural patterns belong to five intergrowths of Fe-Ti oxide minerals such as (1) ilmenite-hematite, (2) magnetite-ilmenite, (3) hematite-rutile, (4) ilmenite-hematite-rutile, and (5) ilmenite-rutile, where ilmenite-hematite intergrowth is common. Alteration is seen in both exsolved and unexsolved ilmenites. Textural patterns and mineral chemistry of the studied ilmenite minerals provide lines of evidence of low-temperature magmatic inheritance, later modified by diffusional processes. The estimated temperature and oxygen fugacity from the magnetite-ilmenite exsolution range from 547.6 to 558.2 °C and from 10^?21.4 to 10^?21.7, respectively. The data are also consistent with hematite-ilmenite temperature (between 537 and 540 °C) and oxygen fugacity (10^?21.7 to 10^?21.9) measurements in Cox’s Bazar beach placers. These temperatures and oxygen fugacities specify Fe-Ti oxide assemblages equilibrated in a T-fO₂ field very near to the FMQ buffer curve suggesting a crustal source (magmatic and/or metamorphic), which is modified significantly by metamorphic processes.     

Physical controls on sand composition and relative durability of detrital minerals during ultra‐long distance littoral and aeolian transport (Namibia and southern Angola)

Sediment in coastal Namibia to southern Angola is supplied dominantly from the Orange River with minor additional fluvial input and negligible modifications by chemical processes, which makes this a great test case for investigating physical controls on sand texture and composition. This study monitored textural, mineralogical and geochemical variability in beach and aeolian‐dune sands along a ca 1750 km stretch of the Atlantic coast of southern Africa by using an integrated set of techniques, including image analysis, laser granulometry, optical microscopy, Raman spectroscopy and bulk‐sediment geochemistry. These results contrast with previous reports that feldspars and volcanic detritus break down during transport, that sand grains are rounded rapidly in shallow‐marine environments, and that quartzose sands may be produced by physical processes. Mechanical wear is unable to modify the relative abundance of detrital components, including pyroxene and mafic volcanic rock fragments traditionally believed to be destroyed rapidly. The sole exceptions are poorly lithified or cleaved sedimentary/metasedimentary rock fragments, readily lost at the transition to the marine environment, and slow‐settling flaky micas, winnowed and deposited offshore. Coastal sediments tend to be depleted in relatively mobile amphibole, preferentially entrained offshore or re‐deposited in sheltered beaches, while less mobile garnet is retained onshore. No detrital mineral displays a significant increase in grain roundness after 300 to 350 km of longshore transport in high‐energy littoral environments from the Orange mouth to south of the Namib Erg, but all minerals get rapidly rounded after passing into the dunefield. Pyroxene and opaques get rounded faster than harder quartz and garnet, but sand mineralogy remains unchanged. Excepting strong transient selective‐entrainment effects, physical processes are unable to modify sand composition significantly. Selective mechanical breakdown can be largely neglected in quantitative provenance analysis of sand and sandstone even in the case of ultra‐long‐distance transport in high‐energy environments dominated by strong persistent winds and waves.     

Regional geoelectric structure beneath Deccan Volcanic Province of the Indian subcontinent using magnetotellurics

Understanding deep continental structure and the seismotectonics of Deccan trap covered region has attained greater importance in recent years. For imaging the deep crustal structure, magnetotelluric (MT) investigations have been carried out along three long profiles viz. Guhagarh–Sangole (GS), Sangole–Partur (SP), Edlabad–Khandwa (EK) and one short profile along Nanasi–Mokhad (NM). The results of GS, SP and NM profiles show that the traps lie directly over high resistive basement with thin inter-trappean sediments, where large thickness of sediments, of the order of 1.5–2.0 km, has been delineated along EK profile across Narmada–Son–Lineament zone. The basement is intersected by faults/fractures, which are clearly delineated as narrow steep conducting features at a few locations. The conducting features delineated along SP profile are also seen from the results of aeromagnetic anomalies. Towards the southern part of the profile, these features are spatially correlated with Kurduwadi rift proposed earlier from gravity studies. Apart from the Kurduwadi rift extending to deep crustal levels, the present study indicates additional conductive features in the basement. The variation in the resistivity along GS profile can be attributed to crustal block structure in Koyna region. Similar block structure is also seen along NM profile.Deccan trap thickness, based on various geophysical methods, varies gradually from 1.8 km towards west to 0.3 km towards the east. While this is the general trend, a sharp variation in the thickness of trap is observed near Koyna. The resistivity of the trap is more (150–200 Ω m) towards the west as compared to the east (50–60 Ω m) indicating more compact or denser nature for the basalt towards west. The upper crust is highly resistive (5000–10,000 Ω m), and the lower crust is moderately resistive (500–1000 Ω m). In the present study, seismotectonics of the region is discussed based on the regional geoelectrical structure with lateral variation in the resistivity of the basement and presence of anomalous conductors in the crust.     

Growth, linkage, and termination processes of a 10-km-long strike-slip fault in jointed granite: the Gemini fault zone, Sierra Nevada, California

Field-based structural analysis of an exhumed, 10-km-long strike-slip fault zone elucidates processes of growth, linkage, and termination along moderately sized strike-slip fault zones in granitic rocks. The Gemini fault zone is a 9.3-km-long, left-lateral fault system that was active at depths of 8–11 km within the transpressive Late-Cretaceous Sierran magmatic arc. The fault zone cuts four granitic plutons and is composed of three steeply dipping northeast- and southwest-striking noncoplanar segments that nucleated and grew along preexisting cooling joints. The fault core is bounded by subparallel fault planes that separate highly fractured epidote-, chlorite-, and quartz-breccias from undeformed protolith. The slip profile along the Gemini fault zone shows that the fault zone consists of three 2–3-km-long segments separated by two ‘zones’ of local slip minima. Slip is highest (131 m) on the western third of the fault zone and tapers to zero at the eastern termination. Slip vectors plunge shallowly west-southwest and show significant variability along strike and across segment boundaries. Four types of microstructures reflect compositional changes in protolith along strike and show that deformation was concentrated on narrow slip surfaces at, or below, greenschist facies conditions. Taken together, we interpret the fault zone to be a segmented, linked fault zone in which geometrical complexities of the faults and compositional variations of protolith and fault rock resulted in nonuniform slip orientations, complex fault-segment interactions, and asymmetric slip-distance profiles.     

Environmental impact of the former Pb–Zn mining and smelting in East Belgium

In the mining district of Plombières-La Calamine (East Belgium), extensive Pb–Zn mining activities resulted in an important contamination of overbank sediments along the Geul river. Moreover, a huge amount of heavy metals is stored in a dredged mine pond tailing, which is located along the river. In the dredged mine pond tailing sediments, Pb–Zn minerals control the solubility of Zn, Pb and Cd. Although Pb, Zn and Cd display a lower solubility in overbank sediments compared to the mine tailing pond sediments, elevated concentrations of Pb, Zn and Cd are still found in the porewater of the overbank sediments. The considerable ‘actual’ and ‘potential’ mobility of Zn, Pb and Cd indicates that the mine pond tailing sediments and the overbank sediments downstream from the mine pond tailing represent a considerable threat for the environment. Besides the chemical remobilisation of metals from the sediments, the erosion of overbank sediments and the reworking of riverbed sediments act as a secondary source of pollution.     

Melonite group minerals and other tellurides from three Cu–Ni–PGE prospects, Eastern Desert, Egypt

Melonite group minerals and other tellurides are described from three Cu–Ni–PGE prospects in the Eastern Desert of Egypt: Gabbro Akarem, Genina Gharbia and Abu Swayel. The prospects are hosted in late Precambrian mafic–ultramafic rocks and have different geologic histories. The Gabbro Akarem prospect is hosted in dunite pipes where net-textured and massive sulfides are associated with spinel and Cr-magnetite. Michenerite, merenskyite, Pd–Bi melonite and hessite occur mainly as inclusions in sulfides. Typical magmatic textures indicate a limited role of late- and post-magmatic hydrothermal processes. At Genina Gharbia, ore forms either disseminations in peridotite or massive patches in hornblende-gabbro in the vicinity of metasedimentary rocks. Actinolitic hornblende, epidote, chlorite and quartz are common secondary silicates. Sulfide textures and host rock petrography suggest a prolonged late-magmatic hydrothermal event. Michenerite, merenskyite, Pd–Bi melonite, altaite, hessite, tsumoite, sylvanite and native Te are mainly present in secondary silicates. The Abu Swayel prospect occurs in conformable, lens-like mafic–ultramafic rocks in metasedimentary rocks and along syn-metamorphic shear zone. The sulfide ore and host rocks are metamorphosed (amphibolite facies; 550 to 650 °C, 4 to 5 kbar) and syn-metamorphically sheared. Melonite group minerals are represented by merenskyite and Pd–Bi melonite. Other tellurides comprise hessite, altaite and joséite-B. Melonite group minerals and tellurides occur as inclusions in mobilized sulfides and along cracks in metamorphic garnet and plagioclase.The different geological history of the three prospects permits an examination of the role played by magmatic, late-magmatic and metamorphic processes on the mineralogy of melonite group minerals and diversity of tellurides. The contents of PGE and Te in the ore and temperature of crystallization control the mineralogy and compositional trends of the melonite group minerals. Crystallization of the melonite group minerals over a wide range of temperatures in a Te-rich environment enhances the elemental substitutions. Merenskyite dominates the mineralogy of the group at low Te activity, while Pd–Bi melonite is the common phase at high Te activity.     

The formation of garnet in olivine-bearing metagabbros from the Adirondacks

A regional study of olivine-bearing metagabbros in the Adirondacks has permitted testing of the P(pressure)-T(temperature)-X(composition) dependence of garnet-forming reactions as well as providing additional regional metamorphic pressure data. Six phases, olivine, orthopyroxene, clinopyroxene, garnet, plagioclase and spinel, which can be related by the reactions: orthopyroxene+clinopyroxene+spinel +anorthite=garnet, and forsterite+anorthite=garnet occur together both in coronal and in equant textures indicative of equilibrium. Compositions of the respective minerals are typically Fo_25–72, En_44–75, En_30–44Fs_9–23Wo_47–49, Pp_13–42Alm_39–63Gr_16–20, An_29–49 and Sp_16–58. When they occur in the same rock, equant and coronal garnets are homogeneous and compositionally identical suggesting that chemical equilibrium may have been attained despite coronal textures. Extrapolating reactions in the simple CMAS system to granulite temperatures and making thermodynamic corrections for solid solutions gives equilibration pressures (using the thermometry of Bohlen et al. 1980b) ranging from about 6.5 kb in the Lowlands and southern Adirondacks to 7.0–8.0 kb in the Highlands for the assemblage olivine-plagioclase-garnet. These results are consistent with inferred peak metamorphic conditions in the Adirondacks (Valley and Bohlen 1979; Bohlen and Boettcher 1981). Thus the isobaric retrograde path suggested by Whitney and McLelland (1973) and Whitney (1978) for the formation of coronal garnet in olivine metagabbros may not be required. Application of the same equilibria gives >8.7 kb for South Harris, Scotland and 0.9 kb for the Nain Complex. Disagreement of the latter value with orthopyroxeneolivine-quartz barometry (Bohlen and Boettcher 1981) suggests that the use of iron-rich rocks (olivines Fa₅₀) results in errors in calculated pressures.Contribution No. 385 from the Mineralogical Laboratory, Department of Geological Sciences, The University of Michigan, Ann Arbor, Michigan 48109, USA     

Petrology of peridotite and garnet clinopyroxenite of the Mt. Higasi-Akaisi mass,central Sikoku,Japan — Subsolidus relation of anhydrous phases

The mineralogy of anhydrous minerals of peridotite and garnet clinopyroxenite of the Mt. Higasi-Akaisi peridotite mass, Japan, is described. The subsolidus equilibria among garnet, clinopyroxene, orthopyroxene and olivine are discussed in terms of composition range of solid solutions and of Fe-Mg partition. It is concluded that the anydrous minerals of this mass equilibrated at lower temperatures than any of well studied peridotite-garnet clinopyroxenite association. The tentative estimation gives 5–600° C and 7–13 Kb as the physical conditions of equilibration. Comparison with similar associations from other occurrences and geological implications are briefly discussed.     

Source geometry and mechanism of 1978 Tabas, Iran, earthquake from well located aftershocks

Aftershocks of the September 16, 1978 Tabas earthquake located from close-in observations made during a four-week fielding of temporary stations have been analyzed for the purpose of delineating detailed source geometry of the 1978 earthquake. Spatial distribution of aftershocks and their composite focal mechanism suggest that the geometry of faulting is far from planar. Aftershocks define two prominent alignment. The southern alignment strikes E-W to WNW-ESE, whereas the northern alignment strikes in a N-S to NNW-SSE direction with an abrupt change of nearly 55–60 degrees near 33.4°N latitude. Both field observations of surface faulting pattern and systematic variation of principal directions of stress axes computed from aftershock focal mechanisms are consistent with the upthrusting and imbrication of a wedge shaped crustal block with the wedge angle of about 120 degrees. Both geological and seismological evidence suggest that the deformed zone is truncated at the southern edge by preexisting E-W fault structures. New observations may provide a partial answer to the unexplained farfield asymmetry of the long period Rayleigh wave radiation pattern recently observed for the mainshock across IDA network.     

Distribution of Indus born mica along Gulf of Kachchh coast: Implications in understanding current dynamics

Indus is one of the major sources of sediments to the Gulf of Kachchh. Yet only its <63 micron fraction is studied in detail with regards to the offshore current dynamics. Hence here we present our study on characteristic signature of the Indus sediment load (i.e. mica minerals) in >63 micron size fraction along the coast of Gulf of Kachchh. The spatial distribution of mica minerals along the Gulf of Kachchh coast was studied which showed in general decreasing trend as we move along the northern and southern coast of the Gulf of Kachchh but, an increase in amount near the southern mouth at Okha. The study shows that the earlier proposed tidal barrier is ineffective in restricting movement of mica across the mouth of the gulf due to its characteristic transport mechanism. Also the presence of mudflats along the gulf of Kachchh coast plays a vital role as sediment receptors in the active sediment transport processes and mica minerals prove to be a promising simple tracer in studying the Indus born sediments in the region.     

Process recognition in multi-element soil and stream-sediment geochemical data

Stream-sediment and soil geochemical data from the Upper and Lower Coastal Plains of South Carolina (USA) were studied to determine relationships between soils and stream sediments. From multi-element associations, characteristic compositions were determined for both media. Primary associations of elements reflect mineralogy, including heavy minerals, carbonates and clays, and the effects of groundwater. The effects of groundwater on element concentrations are more evident in soils than stream sediments. A “winnowing index” was created using ratios of Th to Al that revealed differing erosional and depositional environments. Both soils and stream sediments from the Upper and Lower Coastal Plains show derivation from similar materials and subsequent similar multi-element relationships, but have some distinct differences. In the Lower Coastal Plain, soils have high values of elements concentrated in heavy minerals (Ce, Y, Th) that grade into high values of elements concentrated into finer-grain-size, lower-density materials, primarily comprised of carbonates and feldspar minerals (Mg, Ca, Na, K, Al). These gradational trends in mineralogy and geochemistry are inferred to reflect reworking of materials during marine transgressions and regressions. Upper Coastal Plain stream-sediment geochemistry shows a higher winnowing index relative to soil geochemistry. A comparison of the 4 media (Upper Coastal Plain soils and stream sediments and Lower Coastal Plain soils and stream sediments) shows that Upper Coastal Plain stream sediments have a higher winnowing index and a higher concentration of elements contained within heavy minerals, whereas Lower Coastal Plain stream sediments show a strong correlation between elements typically contained within clays. It is not possible to calculate a functional relationship between stream sediment–soil compositions for all elements due to the complex history of weathering, deposition, reworking and re-deposition. However, depending on the spatial separation of the stream-sediment and soil samples, some elements are more highly correlated than others.     

Thessaloniki–Gerakarou Fault Zone (TGFZ): the western extension of the 1978 Thessaloniki earthquake fault (Northern Greece) and seismic hazard assessment

Active faulting and seismic properties are re-investigated in the eastern precinct of the city of Thessaloniki (Northern Greece), which was seriously affected by two large earthquakes during the 20th century and severe damage was done by the 1759 event. It is suggested that the earthquake fault associated with the occurrence of the latest destructive 1978 Thessaloniki earthquake continues westwards to the 20-km-long Thessaloniki–Gerakarou Fault Zone (TGFZ), which extends from the Gerakarou village to the city of Thessaloniki. This fault zone exhibits a constant dip to the N and is characterised by a complicated geometry comprised of inherited 100°-trending faults that form multi-level branching (tree-like fault geometry) along with NNE- to NE-trending faults. The TGFZ is compatible with the contemporary regional N–S extensional stress field that tends to modify the pre-existing NW–SE tectonic fabric prevailing in the mountainous region of Thessaloniki. Both the 1978 earthquake fault and TGFZ belong to a ca. 65-km-long E–W-trending rupture fault system that runs through the southern part of the Mygdonia graben from the Strymonikos gulf to Thessaloniki. This fault system, here called Thessaloniki–Rentina Fault System (TRFS), consists of two 17–20-km-long left-stepping 100°-trending main fault strands that form underlapping steps bridged by 8–10-km-long ENE–WSW faults. The occurrence of large (M6.0) historical earthquakes (in 620, 677 and 700 A.D.) demonstrates repeated activation, and therefore the possible reactivation of the westernmost segment, the TGFZ, could be a major threat to the city of Thessaloniki. Changes in the Coulomb failure function (ΔCFF) due to the occurrence of the 1978 earthquake calculated out in this paper indicate that the TGFZ has been brought closer to failure, a convincing argument for future seismic hazard along the TGFZ.     

Seismic refraction study of the continental edge off the eastern united states

Three long, strike-parallel, seismic-refraction profiles were made on the continental shelf edge, slope and upper rise off New Jersey during 1975. The shelf edge line lies along the axis of the East Coast Magnetic Anomaly (ECMA), while the continental rise line lies 80 km seaward of the shelf edge. Below the unconsolidated sediments (1.7–3.6 km/sec), high-velocity sedimentary rocks (4.2–6.2 km/sec) were found at depths of 2.6–8.2 km and are inferred to be cemented carbonates. Although multichannel seismic-reflection profiles and magnetic depth-to-source data predicted the top of oceanic basement at 6–8 km beneath the shelf edge and 10–11 km beneath the rise, no refracted events occurred as first arrivals from either oceanic basement (layer 2, approximately 5.5 km/ sec) or the upper oceanic crust (layer 3A, approximately 6.8 km/sec). Second arrivals from 10.5 km depth beneath the shelf edge are interpreted as events from a 5.9 km/sec refractor within igneous basement. Other refracted events from either layers 2 or 3A could not be resolved within the complex second arrivals. A well-defined crustal layer with a compressional velocity of 7.1–7.2 km/sec, which can be interpreted as oceanic layer 3B, occurred at 15.8 km depth beneath the shelf and 12.9 km beneath the upper rise. A well-reversed mantle velocity of 8.3 km/sec was measured at 18–22 km depth beneath the upper continental rise. Comparison with other deep-crustal profiles along the continental edge of the Atlantic margin off the United States, specifically in the inner magnetically quiet zone, indicates that the compressional wave velocities and layer depths determined on the U.S.G.S. profiles are very similar to those of nearby profiles. This suggests that the layers are continuous and that the interpretation of the oceanic layer 3B under the shelf edge east of New Jersey implies progradation of the shelf outward over the oceanic crust in that area. This agrees with magnetic anomaly evidence which shows the East Coast Magnetic Anomaly landward of the shelf edge off New Jersey and with previous seismic reflection data which reveal extensive outbuilding of the shelf edge during the Jurassic and Lower Cretaceous, probably by carbonate bank-margin accretion.     

Geology and mineral potential of Ethiopia: a note on geology and mineral map of Ethiopia

This work presents a geoscientific map and database for geology, mineral and energy resources of Ethiopia in a digital form at a scale of 1:2,000,000, compiled from several sources. The final result of the work has been recorded on CD-ROM in GIS format so that the map and the database could be available to users on a personal computer.Metallic resources (precious, rare, base and ferrous–ferroalloy metals) are widely related to the metamorphic meta-volcano-sedimentary belts and associated intrusives belonging to various terranes of the Arabian–Nubian Shield, accreted during the East and West Gondwana collision (Neoproterozoic, 900–500 Ma).Industrial minerals and rock resources occur in more diversified geological environments, including the Proterozoic basement rocks, the Late Paleozoic to Mesozoic sediments and recent (Cenozoic) volcanics and associated sediments.Energy resources (oil, coal, geothermal resources) are restricted to Phanerozoic basin sediments and Cenozoic volcanism and rifting areas.     

Heavy minerals of the Barakar Formation,Talchir Gondwana Basin,Orissa

Heavy mineral analysis has been carried out in the Barakar Formation of the Talchir Gondwana Bbasin, Orissa. The characteristic heavy minerals are garnet, zircon, tourmaline, rutile, biotite, chlorite, pyroxenes, hornblende, staurolite, sillimanite, apatite, epidote, sphene, spinel and siderite including opaques and leucoxene. These heavy minerals are divisible into four groups on the basis of principal component analysis and suggest derivation of Barakar sediments from pegmatite, acid and basic igneous as well as low- and high-rank metamorphic rocks lying to the south of the Talchir Gondwana Basin. Though the heavy mineral suites of all the sandstone samples are by and large similar, differences have been noticed in the frequencies of many heavy minerals in vertical succession. Cyclic nature and vertical fluctuation of heavy mineral frequencies can be ascribed to variation of the relief of the source area, sudden release of some of the minerals in the source region and/or existence of favourable geochemical condition to escape partial dissolution.