Genesis of the Assif El Mal Zn–Pb (Cu,Ag) vein deposit. An extension-related Mesozoic vein system in the High Atlas of Morocco. Structural,mineralogical, and geochemical evidence

The Assif El Mal Zn–Pb (Cu–Ag) vein system, located in the northern flank of the High Atlas of Marrakech (Morocco), is hosted in a Cambro-Ordovician volcaniclastic and metasedimentary sequence composed of graywacke, siltstone, pelite, and shale interlayered with minor tuff and mudstone. Intrusion of synorogenic to postorogenic Late Hercynian peraluminous granitoids has contact metamorphosed the host rocks giving rise to a metamorphic assemblage of quartz, plagioclase, biotite, muscovite, chlorite, amphibole, chloritoid, and garnet. The Assif El Mal Zn–Pb (Cu–Ag) mineralization forms subvertical veins with ribbon, fault breccia, cockade, comb, and crack and seal textures. Two-phase liquid–vapor fluid inclusions that were trapped during several stages occur in quartz and sphalerite. Primary inclusion fluids exhibit T _h mean values ranging from 104°C to 198°C. Final ice-melting temperatures range from −8.1°C to −12.8°C, corresponding to salinities of ∼15 wt.% NaCl equiv. Halogen data suggest that the salinity of the ore fluids was largely due to evaporation of seawater. Late secondary fluid inclusions have either Ca-rich, saline (26 wt.% NaCl equiv.), or very dilute (3.5 wt.% NaCl equiv.) compositions and homogenization temperatures ranging from 75°C to 150°C. The δ¹⁸O and δD fluid values suggest an isotopically heterogeneous fluid source involving mixing between connate seawater and black-shale-derived organic waters. Low δ¹³C_VPDB values ranging from −7.5‰ to −7.7‰ indicate a homogeneous carbon source, possibly organic matter disseminated in black shale hosting the Zn–Pb (Cu–Ag) veins. The calculated δ³⁴S_H2S values for reduced sulfur (22.5‰ to 24.3‰) are most likely from reduction of SO₄ ²⁻ in trapped seawater sulfate or evaporite in the host rocks. Reduction of sulfate probably occurred through thermochemical sulfate reduction in which organic matter was oxidized to produce CO₂ which ultimately led to precipitation of saddle dolomite with isotopically light carbon. Lead isotope compositions are consistent with fluid–rock interaction that leached metals from the immediate Cambro-Ordovician volcaniclastic and metasedimentary sequence or from the underlying Paleo-Neoproterozoic crustal basement. Geological constraints suggest that the vein system of Assif El Mal formed during the Jurassic opening of the central Atlantic Ocean.     

Accretion and tectono-sedimentary progradation: The Taranto Gulf (Southern Italy)

The geological structures of the eastern Calabrian Apenninic front within the Gulf of Taranto, southern Italy, are compared to those of a convergent margin, using simple criteria such as the origin and volume of the sediment supply, and the relative ratio between sediments carried by the sinking plate and those directly supplied by the overriding margin. Based on this criteria we distinguish four main types of sedimentary accretion occurring at convergent continental margins: (a) Pacific type, (b) Indonesian type, (c) Caribbean type, and (d) Apenninic type.     

Factor analysis: How it copes with complex geological problems

Factor analysis utilizing textural data from 81 bottom samples was used to analyze the surficial sediments covering a 40,000-sq km area, which is one input data point per 500 km. On the other hand, the surficial geology of the area studied is complex as some map units are only 1 km wide in places. Under these circumstances it is interesting to determine that factor analysis nonetheless aims toward a reasonable geological solution. If the premise is accepted that factor analysis provides a solution best-fitted to the data, the geologist has carried his research one step further and is left with the problem of interpreting the results of factor analysis correctly. In this experiment, the interpretation of the factors representing the gravel and the mud is relatively simple, although the two factors representing sands are more difficult to explain. The proper interpretation of factors leads naturally to an inquiry on the optimum number of factors to use, but this problem can be solved objectively by considering the factor loadings.     

Global point‐mass adjustment of the oceanic geoid based on satellite altimetry

Altimeter residuals from a global spherical‐harmonic adjustment of satellite altimetry can be used as observations in a subsequent, or second‐phase, adjustment of a short‐wavelength oceanic geoid in terms of point‐mass magnitudes as parameters. An important part of the development presented is the formulation of the second‐phase adjustment via a banded or a banded‐bordered system of normal equations. This task encompasses three separate features: (1) elimination of the point masses from an observation equation if they are sufficiently far from the pertinent observation point, (2) special arrangement of the point‐mass parameters in the adjustment scheme, and (3) resolution of the resulting system through an adaptation of the well‐known Choleski algorithm. If only the point‐mass magnitudes are subject to adjustment, one is concerned with a banded system of normal equations. If selected tidal parameters are also implicated, this system becomes banded‐bordered. In fact, the former is a special case of the latter in every respect. By virtue of this approach (with or without tidal parameters), geoid undulations over large ocean basins can be adjusted in a few overlapping strips of point masses, leading to a detailed resolution of the entire oceanic geoid.     

Hydrological and geotechnical investigations of mass movements in an equatorial city (Yaoundé, Cameroon)

In the present study, mass movements (landslide and mudslide) bound to a gully located at Mendong, a suburb of Yaoundé in Cameroon were examined using hydrological, geotechnical and geomorphological observations. The data indicate that water is an important causative factor of mass movements in the area studied. In fact, the water flow (waste water and runoff) provokes the saturation of materials at the slope foot. These materials lose their mechanical qualities and some deep ruptures generate landslide. During the rainy season, when the cumulative rainfall is more than 200 mm, these landslides are accompanied by mudslides that generate disturbances on the infrastructure situated around the gully and farther downstream. The economic and environmental damages resulting from the Mendong mass movements are considerable, such as degradation of the topography, losses in farm land, transportation and downstream sedimentation in a pond situated at the slope foot, loss of life and damage to the economy. All this calls for a multidisciplinary and integrated approach to hazard assessment and risk mitigation, which included data collection and interpretation, growing public and authority awareness, and preventing or reducing runoff and waste water flows by proper management and drainage.     

Mineral resources inventory in the northern part of haiti: A basic rationale for selecting areas of potential mining interest

Agriculture has always been the major source of income of the Republic of Haiti. Only in the late sixties did the Haitian Government decide to move toward industrialization and explotation of natural resources, but no reliable inventory of mineral potential was available. In June 1970 the Resources and Transport Division of the U.N. (now CNRET) undertook a structural analysis of the Caribbean with reference to defining favorable loci for ore disposition. One of the conclusions of this survey was that from the metallogenetic point of view, the Northern part of Haiti was a favorable area for prospecting for habe metal deposits, especially for copper. Those conclusions were acknowleadged with great enthusiams by the Haitian authorities, and they welcomed in July 1971 a UN technical adviser who outlined a first phase of exploration. Following this mission, a “Mineral exploration Project” was created by the Haitian Government with the cooperation of UNDP, and an area of 9000 km² was selected, based on structural, lithological, and metallogenetic reasons, as an exploration target. The most important aspects of this project were:Mineral Exploration—First Phase (1973–1974). The following operations were carried out by a small team: (a) photo interpretation at 1:50,000 and 1:200,000 scale, (b) geological reconnaissance at 1:50,000 scale, (c) geochemical reconnaissance (stream sediment) at 1:50,000 scale. The photo interpretation helped outline zones of particular structural interest and was followed up by ground control studies. Stream sediment geochemical reconnaissance was carried out over half of the project area, following the indications given by the photo geological interpretation. finally, combining all the data, five areas were selected for detailed follow up survey: (1) Terrier Rouge—Perche, (2) Vallieres, (3) Mont-Organise, (4) Limonade, (5) Gros Morne—Le Borgne.Mineral Exploration—Second Phase (1975–1976). The main zones of interest were reduced to a few hundred km² and porphyry copper type deposits appeared to be the most promising target. Detailed geological mapping (1:25,000 to 1:2,000) and soil geochemistry were carried out on the above mentioned five areas, the most promising appearing quickly to be Terrier Rouge-Perges, with porphyry-type copper mineralization. A geophysical survey (IP and Mag) confirmed the geochemical results. At the end of the second phase of exploration (December 1976) two of the five prospects of the Terrier Rouge area have been diamond drilled and appeared to be of potential economic interest. Because of the number and importance of the prospects discovered a third phase of exploration was deemed necessary with the purpose of continuing the detailed prospection work and drilling the other prospects. This third phase started in January 1977 and was expected to last until December 1979. This paper was presented at the International Geological Correlation Program (IGCP) Project 98: “Standards for Computer Applications in Resource Studies” held at Taita Hills, Kenya, November 8–15, 1977.     

Real-time sea-state surveillance with Skywave Radar

To extract sea-state information from the ionospherically distorted echoes received by a skywave radar, we use a signal-processing strategy that permits real-time decisions about the quality of incoming data. This paper explains the need for an on-line processor and describes some of its engineering details. We use an array processor to quickly compute all the spectra required to display ocean waveheight, as well as some indices of data quality, while the radar interrogates an ocean cell. The results are shown in a test using an experimental radar that mapped waveheight over its North Pacific coverage area. Coverage efficiency was 85 percent, and the radar's waveheight estimates averaged 2ft(0.6 m) higher than those forecast by a numerical model.