Geothermal Exploration in Some Interest Geothermal Area in Republic of Yemen

The first geothermal area (Al Lisi–Isbil Geothermal field) is located about (100) km from Sana’a capital city of Republic of Yemen, and the second geothermal area (Alsyani – Algandeah Geothermal field) is located about (250) km from Sana’a capital city of Republic of Yemen. In addition, the third geothermal area (Red Sea geothermal area) is located about (290) km from Sana’a capital city of Republic of Yemen. The geothermal mapping was carried out in (Al Lisi and Isbil and Alsyani – Algandeah Geothermal field) in the western area of Yemen. The rocks type in Al Lisi–Isbil Geothermal area was classified To six group, trap series, the post trappic volcanic activity, Isbil volcanic complex, Al Lisi volcanic complex, Basaltic Fissure volcanism and recent and active sedimentary deposits, The main structural feature are trend (NNE-SSW), (NE-SW),The rocks type in the second geothermal area Alsyani – Algandeah Geothermal area was classified to (4) type of Rocks, Tertiary Volcanic (Basalt, Rhyolite, and Tertiary intrusive rocks), Tawilah Sandstone Group, Medj-Zir Sandstone and Quaternary Deposits. The main structural feature is trend (NE-SW). In Al Lisi and Isbil Geothermal area The Geothermal manifestations (steam, clay alteration and slight alteration)common in many deferent site in the Geothermal area, two types of alteration zones are distinguished slight alteration mostly characterized by slight color change of the Brownish, reddish, yellowish to white colors and also involving some silica minerals (opal) and calcite veins and the some altered rocks assume a whitish color due to the presence of opline silica, clay minerals and iron oxides. In addition, the Albit, Montomornillonite, Biotite, Kaolinite, Chlorite Quartz, and Calcite are the individual minerals obtained by analysis (X-Ray) for samples taken from Al Lisi and Isbil Geothermal area. The temperatures of steam that exceed 92°C and They are 118 hot well in the area the temperature between (25°C) to (59°C). And the Geothermal manifestations(slight alteration)In Alsyani–Algandeah Geothermal area are common in many deferent site in the Geothermal field, one types of alteration zones are distinguished slight alteration mostly characterized by slight color change of the Brownish, reddish, to yellowish colors and also involving some silica minerals (opal) and calcite veins and the some altered rocks assume a Brownish, reddish and yellowish color due to the presence of opline silica, calcite veins, clay minerals and iron oxides. In addition, the limonite, Heulandite, Quartz, and Calcite are the individual minerals obtained by analysis (X-Ray) for samples taken from Alsyani–Algandeah Geothermal area. They are (42) hot well in the area the temperature between (27°C) to (75°C), the thermal wells to 340 meters deep (75°C), are in the area. Also The Red Sea geothermal area is located in west area of western Yemen volcanic part, was covered by drilling is does not exceed 3000 km2,but data from several areas throughout the world, including neighboring countries such as Ethiopia yielded similar temperatures and geothermal gradients. In the Present, the temperature logs from the boreholes show temperatures of 190°C at 2458 m depth in the Red Sea geothermal area.


INTRODUCTION 1-Objective of the Study
The main goals of this study were to Explored the geothermal energy resources and to make geological and geothermal maps of a volcanic field and tofind out if a relationship could be established between the tectonic setting and the geothermal manifestations of the study area.
The geological mapping exercise was carried out in 2010 in the first geothermal area (Al Lisi-Isbil Geothermal field) and in 2012 in the second geothermal area (Alsyani -Algandeah Geothermal field), Instruments and tools used to carry out the fieldwork included the following: A Garmin -GPS 72 to locate and track the structural, stratigraphic and alteration features such as faults, fractures, dykes, stratigraphic boundaries, and alteration zonation. Satellite image and compass used to trace the aerial extent of the major structures and their strike and dip directions and distribution within the study area. A geological hammer, a metric tape and a hand lens used for field inspection of rock samples and unit thicknesses. A shovel, and small plastic sample bags to collect samples from the different alteration zones and different rock units for XRD and petrographic studies, in order to figure out the degree of alteration and the mineral assemblages that exist in the hydrothermally altered areas, and also to differentiate and correlate the different rock units from outcrop to outcrop in the study area.

THE FIRST GEOTHERMAL AREA (AL LISI-ISBIL GEOTHERMAL FIELD) 2-1 Study area
Al Lisi-Isbil Geothermal field is located about (100) km from Sana'a capital city of Republic of Yemen.

2-2 PREVIOUS OF work
The area has been explored intermittently by many geoscientists work. The Exxon Company planned to drill exploration production well in Rosabah area. The well was drilled to provide geologic information regarding the potential for hydrocarbon source, reservoir and seal in the in the Dhamar Basin the programmed depth of goof (or shallower basement). Was not reached because the well wall was still drilling volcanic rock at 5331ft. The well drilled alluvium to depth of 105f (KB), then to total depth a complex of alternating interbedded layers of subaerial basalt flows, basaltic ash flows, basaltic sills, acid tuffs, rhyolitic flows, and possible cinder cones, Numerous subaerial erosion surfaces were recognized but no sediments or reworked clastic sediment were present the volcanic are presumed to be oligo -Miocene in age. The highest bottom hole temperature recorded was 220•f, the extrapolated equilibrium bottom hole temperature is 232•f demonstrating a high thermal gradient and heat flow [2].
In the period January 81 -January 82, ElC Electro consult under an agreement with Yemen oil& minerals Resources corporation performed geoscientific investigations in the Dhamar -Rada'a area with the aim of assessing, at a prefeasibility level, the possible geothermal potentiate of the area. Geochemical thermometry of the waters emerging in the Dhamar-Rada'a area gives somewhat scattered ((numbers)) [2]. Although the maximum temperature so calculated may well be above 200 C [2]. Geochemical anomalies give a consistent pattern, indicative of more permeable zones and higher temperature, in the area of the depression (graben?) extending from the Al Lisi volcano to the ESE, Passing just to the south of the Isbil volcano [2]. On the floor of this depression, this outcrop depression, these outcrops trap souses basalts through the overlying quaternary volcanic, and there exists Avery high concentration of sputter cones. This localized area is structurally quite favorable for the slow upwelling of any warm waters from the depths [2].
The Dhamar Rada'a volcanic field covers an area of about 1477.1 km 2 . The region is characterized by both central and fissural activities and has been affected by intensive vertical tectonism, resulting in the formation of horst and graben structural patterns. It is also characterized by a sequence of pyroclastic flow deposits (ignimbrites), which are widespread on the floor of the graben. Outpouring of basalt through fissures locally followed this explosive activity (basalt). Subsequent central activity produced cones, ash rings and pyroclastic fall deposits. The explosive activity was followed by the extrusion of two rhyolitic lava domes and the formation of an ash ring.

2-3 Some Geochemical Results
During two missions carried out in February 2001 and December 2002, almost all known thermal emergences of continental Yemen, including thermal springs, fumaroles and several CO 2 -rich gas vents, were sampled and analyzed for major, minor and some trace components. Further, some isotopic ratios: 18O/16O and D/H in water samples, 13C/12C in CO 2 (in DIC=dissolved inorganic carbon and free gas) and some 3He/4He ratios (in the free gas phase) were measured (Minissale et al, 2010).
An example of the first situation in the T-depth diagram of Figure (2) could be represented by the well sample # 64, where an apparently very high gradient of 370 °C/km can be estimated in a well, which is only 60 m deep, but with a relatively high temperature of 37 °C. An example of the second situation (excessive cooling from cold rainfall infiltration) in Fig (2) could occur in the well sample # 105, where the measured temperature of water is as low as 26 °C at about 250 m depth, generating an apparent thermal gradient as low as 41 °C/km, just a little higher than the average Earth gradient (33 °C/km) (Minissale et al, 2010).
Apart from this area, there are six additional closed thermally anomalous areas in Figure (3) where the calculated temperature at 1,000 m should be above 120 °C. In total, the area where temperature at 1,000 m should exceed 100 °C is likely to exceed 200-250 km 2 , a very large area that suggests that the deep geothermal system is large (Minissale et al, 2010). According to our interpretation of thermal and chemical data for a large number of wells drilled around the city of Dhamar, we believe that the thermal anomaly in this area is not caused by regional convective fluid circulation of deep fluids ("intracratonic fluids"; Minissale et al., 2000), but rather is caused by local high conductive heat flow. The conductive high heat flow is undoubtedly related to the presence of the magma associated with the Quaternary volcanic, still under cooling. This magma chamber(s) have possibly generated active hydrothermal systems inside the sedimentary substratum, at the base, or inside the YTS volcanic sequence. The platform limestone series of the Amran-Tawila groups, if present in the horst described in the Dhamar area (Chiesa et al., 1983), might be best place to generate the ascending brunch of such hydrothermal system. The anomalous heat flow of the Dhamar aquifer might be the shallow manifestation of such deep convection. Unfortunately, typical chemical components of active hydrothermal systems (NH 4 , B, CO 2 vents, H 2 etc.), in both gas and liquid phases, are missing at the surface. Therefore, the presence of an active hydrothermal system, although probable, can only be speculated (Minissale et al, 2010).
From a geothermal viewpoint, the hypothesized hydrothermal system could be well sealed (e.g. by silica precipitation), thus preventing escape of chemical components to the surface. Our computed geothermal gradients suggest temperature gradients exceeding 100-120 °C/km in several places. Although these gradients cannot be extrapolated to define a clearly assessed geothermal reservoir below the volcanic cover, the area between the Al Lisi and Isbil craters represents a promising area for the drilling of a geothermal exploration well (Minissale et al, 2010).

2-4 Geophysics studies
The result of technical geophysics work give ISO-resistivity contour map. Figure (4) show the anomalies low resistivity zone is located in meddle part of study area.

2-5 Update the geological map in the first geothermal area (Al Lisi-Isbil Geothermal field)
2-5-1 Forming the main layers of the digital maps.
Transfer the data and base maps from Raster to vector data. Digitizing the main layers of the maps.  The Trap Series The Trap series in the area mapped occurs as isolated outcrops bordered ether by recent and actual sedimentary deposits or by post trap basaltic volcanic. It is generally horizontally lying and has been disjointed by vertical tensional tectonic forces without tilting of the blocks. The trap series outcropping in the area mapped is made up mostly of basaltic rocks, which are often deeply weathered.
These rocks are overlain in places, above an erosional surface, by a thick sequence of pyroclastic pumice flow deposits with different degrees of welding (ignimbrites). The post Trappic volcanic Activity The post -Trappic volcanic activity is represented by central and fissure volcanism. The central volcanism consists of volcanic complexes, central apparata, lava domes and explosive craters. The fissure volcanism is characterized by wide spread basaltic lava fields and numerous, scattered spatter cones. Its main activity is definitely younger than the central volcanism. The complex, interlayered nature of the surface features of both lava flows and spatter cones indicate that the volcanic activity occurred over a long time span.
Central Volcanism Plinian Fall Deposits Scattered outcrops of plinian fall deposits reaching maximum thickness of about 6m represent the oldest products of the central volcanism. They consist of angular pumice clasts with maximum observed diameter between 15 and 20cm. They contain unsupported lithic clasts (ømax 60cm) mainly of Crystalline Basement rocks (gneiss, micschist, amphibolite's, pinkish granite) and subordinately of pinkish violet rounded quartz fragments of the Tawilah Group. The areal distribution of the outcrops and the variation in grain size of both pumice and lithic fragments indicate that they belong neither to the same eruption nor to the same vent. The latter cannot be located due to the lack of significant field evidence.

Isbil Volcanic Complex
The Isbil is a complex strato volcano made up mainly of lava flows and subor dinate ignimbrite sheets and pyroclastic fall deposits. It was partially destroyed by a caldera collapse leaving an exposed wall 100m high. The lava flows have compositions ranging from trachytic to rhyolitic. Porphyritic units, maybe linked to dome or crypto dome effusive activity, generally represent the first. The rhyolites are generally micro cry's talline glassy rocks with fluid and convolute textures; sometimes they are vesciculated, producing pumiceous textures. The ignimbrites generally occur as non-welded pumice flow deposits. They occur definitely in the latest stages of the volcanic activity and possibly in the early ones also. In particular, the oldest are ash and pumice flows with a continuous basalt layer of collapsed pumice and elongated obsidian fragments. Small pyroclastic fall and surge deposits occur in the upper part of the edifice. After the formation of the caldera and following NNW-SSE tectonic trends, there followed a volcanic activity mainly represented by domes. In particular, the Hamman Isbil dome was built up on an older tuff cone. A basaltic fissure one with the formation of lava flows and spatter cones followed this silicic volcanic activity.

Al Lisi Volcanic Complex
The Al Lisi volcanic complex is composed of a tuff ring, lava domes and by a tuff cone with a final effusive activity; 2.5 km south of this complex there occurs an explosive crater. The tuff ring consists of surge and fall deposits of slightly vesciculated glass clasts. The domes occurring west of the Al Lisi village consist of black rhyolitic obsidian with a high luster and breaking with a conchoidal fracture. At times, the obsidian is vesicular and shows fluidal texture. The first activity of the Al Lisi volcano is represented by a deeply weathered rhyolitic flow with fluidal and auto clastic texture, irregularly vesciculated. Periods of intensive explosive activity were followed by the formation of about 300 m of pyroclastic surge and fall deposits. They contain only juvenile vitreous clasts with different degrees of vesciculation. In the basal pumice fall deposits one finds lythic fragments, in the centimeter size range, derived mainly from the Crystalline Basement and subordinately from the Trap Series. Erosional surfaces and angular unconformities have been recognized in this pyroclastic succession. A 30 m thick auto clastic rhyolitic obsidian flow with fluidal texture and irregularly vesciculated represents the last manifestation of the volcanic activity. The explosive crater south of Al Lisi due to a phreatic eruption; no juvenile ejecta have been found. It has an irregular elliptical shape with axes of about 200 and 500 m. Its bottom is flat and covered by soils. A low sill about 10m high surrounds the crater, with outer slopes gentler than the inner ones. Basaltic Fissure Volcanism Basaltic fissure volcanism includes widespread basaltic lava fields and numerous, scattered spatter cones. From the morphology, it appears they were formed over a considerable time span: deeply eroded surfaces together with nicely preserved aa or ropy pahoehoe surfaces and nice spatter or cinder cones have been observed. Some of these cones have given rise to small effusive activities. The basaltic lava flows are thin, wide spread and have been strongly controlled by the existing morphology because of their fluidity at the time of eruption. Shorter and thicker flows of more viscous lava have not been found. The volcanism was only of a fissural nature: according to the spatter cones alignments and flow directions of the lavas, the main feeding fractures trend NNE -SSW and E-W.

2-6 Structural of the first geothermal area (Al Lisi-Isbil Geothermal field)
The structural feature in the study area is controlled by the tensional tectonics. The Structural feature were mapped in the study area.   Hydrothermal alteration is a general term embracing the mineralogical, textural, and chemical response of rocks to a changing thermal and chemical environment in the presence of hot water, steam, or gas.

2-7 Geothermal mapping work in the first geothermal area (Al Lisi-Isbil Geothermal field)
The Hot spring, femoral Travertine deposits and hydrothermal alteration zones an extremely important element in geothermal exploration. Although springs are the most obvious surface manifestations of the hydrothermal system, alteration zones supply additional information that points out the areas of greatest temperature and permeability. Alteration zones can also guide exploration geologists to hidden systems or to ancient spring activity. The mapping process involves systematic sampling across the study area and analysis of mineral phases by x-ray diffraction and petrography. Study area can range from a map, which will often show the relationship of geothermal manifestation to Geological features. Figure (6) shows a Map of geothermal manifestation in the area they are to site of geothermal activity in the area. The first one is located in Al Lisi volcanic mountain the temperature (89 º C), and the second site of fumarole is located in Isbil volcanic mountain the temperature (43 º C) and they are 118 well in the area the temperature between (21ºC) to (59ºC) and the depth between 40 m to 350 m. The rocks show hydrothermal alteration from low intensity (slight alteration), to clayish alteration witness formerly active fumaroles, where the volcanic rocks have been completely replaced by secondary minerals.

2-7-1 Geothermal manifestations
The geothermal manifestations are common in Al Lisi volcanic mountain, West and North West of the Al Lisi Mountain, Isbil volcanic mountain and South and east of the Isbil Mountain. Two types of alteration zones are distinguished slight alteration mostly characterized by slight color change of the Brownish, reddish, yellowish to white colors and involving some calcite veins and the altered rocks assume a whitish color due to the presence of opline silica, clay minerals and iron oxides. The clayish alteration witness formerly active fumaroles where the host rock has been completely replaced by clay. Hydrothermal surface alteration, hot or cold, indicates the presence of a hydrothermal systems beneath at some time therefore, mapping the surface alteration is useful in delineating a hydrothermal. The alteration intensity increases with increasing activity. By distinguishing between unaltered rocks (fresh or weathered) and slightly hydrothermally altered rocks, one can make destination .Intensive hydrothermal circulation has produced vapour phase crystallization and has induced deep alteration in the vitreous mass.  Figure 6: The Geothermal map of the first geothermal area (Al Lisi-Isbil Geothermal field) Slight alteration As the hydrothermal activity widespread in the mapped area, a considerable part of the rocks in the field area is slightly altered or visibly affected by some thermal alteration.
Clay alteration Extinct clay alteration is less common than the slight alteration Figure (7) shows clay alteration

2-8 Mineralization
Thin calcite veins are found in the east and south of Isbil Mountain. The basalts rock shows extensive calcite veining Figure (8). Very small occurrences of cinnabar and regular have also been found [2]. The silica minerals (opal) are found in the west of Al Lisi Mountain. The presence and distribution of such indicate the existence of wide fossil geothermal filed northwest of the Al Lisi volcanic complex [2].The, most common epithermal alteration styles are origillization relied to rhyolite domes in other areas, the predominant alteration styles are orgillization and pyritization related to quartz veins. Advanced orillic alteration as well as potassic alteration in the form of secondary biotite are identified at wavagaha area (Mattash et al, 2010). Sulfide mineralization observed was almost all pyritic or limonitic Gangue minerals were either quartz (veins, stockworks, or epithermal breccia matrices), calcite or clay (vein selvages or argillic zones) (Mattash et al, 2010). Nevertheless, as along the Thamarwaragah -Jabal Al Lisi trend, opalitic alteration can be the uppermost expression of a preserved epithermal vent, and thus provide valid targets for epithermal exploration (Mattash et al, 2010).

3-THE SECOND GEOTHERMAL AREA (ALSYANI -ALGANDEAH GEOTHERMAL FIELD) 3-1 Study area
Alsyani -Algandeah Geothermal field is located in southern part of the west area of Yemen about (250) km from Sana'a capital city of Republic of Yemen.

3-3 Structural of the second geothermal area (Alsyani -Algandeah Geothermal field)
The structural feature in the study area is controlled by the tensional tectonics. The Structural feature were mapped in the study area. The main structural feature trend (NE-SW). Figure's ( 11 ) shows a Map of geothermal manifestation in the area The geothermal manifestations are common in many site in the Geothermal field , one types of alteration zones are distinguished slight alteration, mostly characterized by slight color change of the Brownish, reddish, yellowish to white colors and also involving some silica minerals (opal) and calcite veins and the some altered rocks assume a whitish color due to the presence of opline silica, clay minerals and iron oxides. They are (42) hot well in the area the temperature between (27ºC) to (75ºC) and the depth between 200 m to 600 m.

Slight alteration
As the hydrothermal activity widespread in the mapped area, a considerable part of the rocks in the field area is slightly altered or visibly affected by some thermal alteration Figure (12) shows Slight alteration.

3-5 Mineralization
Thin silica minerals (opal) and calcite veins are found in many deferent site in the study area. The basalts rock shows extensive silica minerals (opal) and calcite veining (Figure 13). The ziolite minerals are found in the southern part of the study area

4-2 Geological of the third geothermal area (Red Sea geothermal area)
The Red Sea area covered by drilling is does not exceed 3000 km 2 , but data from several areas throughout the world, including neighboring countries such as Ethiopia yielded similar temperatures and geothermal gradients. In addition, the physical convective anomaly beneath Yemen (volcanic province) that is detected by space imagery (USGS, 1994) still is one of the most important in the whole region of the Afro-

4-3 Heat flow in the third geothermal area (Red Sea geothermal area)
The present geothermal gradient in the Red Sea region ranges from 49 to 77 C/km, and the present heat flow varies from 94 to154 mW/m2. In support of this claim, data are obtained from several oil and gas wells drilled to 2458 meters deep. In the Present, the temperature logs from the boreholes show temperatures of 190°C at 2458 m depth in the Red Sea geothermal area, Figure (15).   Figure 15: Example of the geothermal gradient of the third geothermal area (Red Sea geothermal area)

CONCLUSIONS
The first geothermal area (Al Lisi and Isbil Geothermal field) is located in medal part of western Yemen volcanic part. It is particular is not a stable continental zone, it is characterized by some indication of elevated crustal magmas and thermal phenomena related to deep crustal fracture systems. The rocks in the study area classified to (6)   on the geothermal map, slightly alteration. And The Red Sea geothermal area is located in west area of western Yemen volcanic part, was covered by drilling is does not exceed 3000 km 2 , but data from several areas throughout the world, including neighboring countries such as Ethiopia yielded similar temperatures and geothermal gradients. In the Present, the temperature logs from the boreholes show temperatures of 190°C at 2458 m depth in the Red Sea geothermal area.