Mineralogy of The Beach Sands Along the Mediterranean Coast from Benghazi to Bin-Jawwad, NE Libya

The present work aims to characterize the mineralogy of the beach sands along the Mediterranean Coast from Benghazi to Bin Jawwad, NE Libya. The microscopic and SEM examinations indicate an abundance of carbonates, quartz, feldspars, and evaporites. The detected heavy minerals are zircon, tourmaline, pistachite, hornblende, garnet, monazite, rutile, titanite, augite, biotite, kyanite, chromian spinel, magnetite, ilmenite


Introduction
The present work describes the mineralogy of the beach sands along the Mediterranean Coast from Benghazi to Bin Jawwad, NE Libya.The study area is the coastal area of a part of the Sirte Basin (Figure 1).The Sirte Basin ranks the 13 th among the world's petroleum provinces, having proven oil reserves estimated at 43.1 billion barrels of oil equivalent, an amount that constitutes 1.7% of the world's known oil reserves.The basin consists of one dominant total petroleum system, known as the Sirte-Zelten.According to Mresah (1993), the Sirte Basin of Libya is a Mesozoic-Tertiary rift basin comprising a series of horsts and grabens, which were formed as a result of the collapse of an N-S trending arch in the Upper Cretaceous time.The major structural elements of Libya suggest that the Caledonian uplift is trending N-S to NW-SE while the Hercynian structural elements are trending E-W to NE-SW (Figure 2).The collapse of the Hercynian Tibesti-Sirte uplift during the Triassic-Jurassic led to the development of Sirte basin during the Early Cretaceous.The exposed stratigraphic section in the study area consists of sedimentary rocks, ranging in age from Tertiary to Quaternary (Figure 3).The most abundant sedimentary facies are carbonates with lesser amounts of mudrocks, sandstones, and evaporites.Quaternary deposits disseminate around study area along the beach line.They occur as sand dunes, red soil (terra-rossa), conglomerates, calcarenites and sabkha sediments.All sampled stations in the study area are open beaches.There are two beach types; rocky and sandy beaches (e.g., Bin Jawwad and Aqaylah, respectively, Figure 4).Figure 3. Geological map of the area (scale 1:1,000,000) between Benghazi and Bin Jawwad, NE Libya (modified after Francis and Issawi, 1977;Innocent and Pertusati, 1984;and Mresah, 1998)

Methodology
Samples were collected from the beach sands along the Mediterranean Coast from Benghazi to Bin Jawwad, NE Libya, from 25 stations (four samples of each station) at sampling interval between 10 and 20 km, depending on accessibility to the studied beach.The traverse is parallel to the studied coast.Samples were essentially taken from the surface sands to represent the uppermost 30 cm of the beach sands.
The present study is a detailed mineralogical investigation on the very fine and fine sand size fractions (125-63 μm, and 250-125 μm) of the beach sands under consideration.The two size fractions subjected to gravitational heavy mineral separation using bromoform (specific gravity 2.87).The fractions of both the light-and heavy-minerals mounted in Canada balsam for transmitted light microscopy.
Scanning electron microscope with an energy dispersive X-ray attachment (SEM-EDX) used to shed light on the geochemical characteristics of the mineral composition.In spite of the fact that EDX microanalysis extensively used in the present work, its output was not quoted herein because of their standard-less and semi-quantitative nature.The weight or molecular ratios of major oxides used to express the possible changes in composition.The X-ray powder diffraction of whole samples used to estimate the relative abundance of calcite and aragonite as main partners of the carbonate fraction.

Light Minerals
The distribution and morphological properties of light minerals have persuaded many geoscientists to study them with respect to depositional environment and provenance (Trevena and Nash, 1979;Carranza-Edwards et al., 1998;and Margineanu et al., 2014).The studied beach sands are a mixture of carbonate and non-carbonate materials.The microscopic examination and the X-ray powder diffraction of whole-sediment samples indicate an abundance of carbonates, quartz, feldspars and evaporites with other minor minerals.Figures ( 5 and 6) demonstrate the relative frequency of the light minerals in both the fine and very fine sand fractions.

Carbonates
According to Schwartz (2005), carbonate beaches have a significant proportion of the sediment fabric of biogenic origin, and carbonate in composition.Carbonate beaches are, therefore, wave deposited accumulations of sediment (sand to boulder in size) deposited on shores where a near shore supply of biogenic debris is available.Carbonate beaches exist in tropical and temperate locations, including some in relatively high latitudes.The main prerequisite for a carbonate beach is a source of carbonate-producing detritus, and a mechanism to erode and/or transport it to the shore.In the studied samples, the recorded carbonate grains include biogenic grains made of aragonite and/or calcite with sporadic dolomite.Calcite is usually colorless and exhibits gleaming interference colors of very high orders (Figure 7).It occurs in form of rounded to subrounded monocrystalline grains (Figure 8) and rounded polycrystalline grains (micrite lumps).Disseminated rhombohedral calcite grains are rarely encountered in the studied samples.The micrite calcite grains are thought to be the product of the mechanical breakdown of the micrite envelopes of recent shell fragments, while rhombohedral calcite grains are thought to be of detrital origin (e.g., Anirudhan and Thiruvikramji, 1991;and Luzar-Oberiter et al., 2008).Biogenic grains are composed of whole shell fragments of macrofauna (mollusks) and microfaunal shells, mostly of foraminifera and algae and other, not clearly classifiable biogenic fragments.The EDX microanalysis of a large number of aragonitic and calcitic specimens suggests that the latter is more capable of hosting more inclusions than the former.These inclusions have different composition but those of barium sulfate and phosphates are abundant (Table 1).The difference in the composition of the inclusions may suggest derivation from various provenances.According to Tucker (2001), the requisite Mg/Ca ratios are < 1.2 for low-Mg calcite, 1.2 -5.5 for high-Mg calcite, and > 2 for aragonite.Generally, high-Mg calcite and aragonite are the predominant mineralogies of organisms in modern seas (Mg/Ca ratio=5.2, as quoted by Zankl, 1993).The EDX microanalysis shows that all analyzed grains are low-Mg calcite (see Table 1).Pyokari (1997) and El-Werfalli (2016) stated that low-Mg calcite is the most common mineral in the carbonate beach sands.That speciation is rather due to diagenetic transformations of the carbonate material (Preda and Cox, 2005).In the western part of the study area, sands display green color most probably due to algal activity (Figure 9).The XRD analysis (Table 2) shows that in the central and eastern sides of the studied beach, aragonite dominates over calcite.This feature is possibly related to a number of regional characteristics such as biological production.In the western section calcite dominants over aragonite.That speciation is rather due to diagenetic transformations of the carbonate material.In agreement with Preda and Cox (2005), carbonate speciation suggests a difference in sediment age; the central and eastern sides consist of younger sediment, while older, reworked, and diagenetically transformed materials dominate in the western section.

Quartz
In the studied beach sands, quartz is commonly colorless and contains inclusions, namely, tourmaline (see Figure 7), rutile, and apatite.It is mostly monocrystalline with uniform and undulatory extinction.However, some samples contain polycrystalline quartz grains.It is important to notice that abrasion during transportation may affect the relative abundance of the polycrystalline and undulatory quartz because they destroy preferentially relative to nonundulatory monocrystals (Lewis, 1984).According to Cherian et al., (2004), the reduced

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ISSN: 2413-5267 percentage of the polycrystalline quartz is probably due to dilution by a fresh supply of monocrystalline quartz.Moreover, the polycrystalline quartz grains may disintegrate during the course of transportation from source.The detected quartz grains vary from very angular to well-rounded with relative preponderance of the former type.According to Shine (2006), the rounded and well-rounded quartz grains owe their shape largely to a longer distance of transportation and/or the multi-cycle origin of clastic sediments.On the other hand, moderate to high degree of sphericity of the quartz grains are an indication of derivation from crystalline and older sedimentary rocks exposed in regions far from the basin of deposition (Rahman et al., 2004).The presence of dust rims in most quartz grains as an indicator for sediment recycling has long been recognized (e.g., Dickinson and Milliken, 1995).Some quartz grains show cracks, which could be either due to inheritance from source material or due to long transportation distance.

Feldspars
In the present study, microcline and members of plagioclase series are common feldspars.Microcline is mainly colorless rectangular, in few cases, the microcline grains are altered and turbid (see Figure 7).Plagioclase feldspars occur mainly as fresh grains.

Evaporites
In the studied sands, the detected evaporites are gypsum and halite (Figure 10).Gypsum occurs as prismatic, nodular, tabular and lenticular grains.The fabric and texture of gypsum grains suggest their authigenic crystals.Halite crystallizes together with gypsum.It is frequently recorded some zircon and Ti-minerals as tiny inclusions.

Heavy minerals
The microscopic investigation documents that some minerals such as kyanite and titanite occur exclusively in the western part of the study area.Hornblende, pistachite and garnet

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ISSN: 2413-5267 disappear in the eastern part, whereas zircon, tourmaline, monazite, augite, biotite and rutile exist in the whole area under consideration.

Zircon
Zircon represents the most abundant heavy mineral among the non-opaques.Microscopic observations of zircon enabled the recognition of different shapes of zircon, such as; the oval with zoned structure, elongated, elliptical, outgrown, overgrown, rounded and broken (Figure 11).It generally contains different amounts of inclusions as well as vacuoles or bubbles.
Well-developed fractures crisscrossed the zircon grains might probably be due to their sustained transportation by waves and currents (e.g., Angusamy and Rajamanickam, 2000).It is important to notice that the outgrown and broken zircon grains are copiously present in the very fine sand fraction.According to Angusamy et al., (2004), the prolific presence of broken zircon in the beach sand of southern coast of Tamil Nadu, east coast of India, indicate rigorous energy conditions by waves, due to repeated swash and backwash and by littoral currents.The same authors added that outgrown zircon might be due to the longer stay of sediments in the depositional environment.Some of the examined zircon displays evident metamictized nature (Figure 12).Based on the semi-quantitative EDX microanalysis data (Table 3), there are two types of zircon in the studied samples; the first type is uranium and thorium enriched whereas the second is yttrium and heavy rare earth elements enriched.This suggests the possibility of zircon from different provenances.

Tourmaline
It is the second common non-opaque mineral.Zircon is present in higher frequencies in very fine-grained sediments, whilst tourmaline dominates in fine-grained sands.This observation coincides with that quoted by Sallun and Suguio (2008) in their study on Quaternary deposits from Sao Paulo State, Brazil.This can be attributed to differences in the hardiness of these minerals.Most of the tourmaline grains are surrounded to well-rounded but sometimes prismatic in shape.The authors believe that the occurrence of a rounded to well-rounded tourmaline variety suggests recycling from the older sedimentary precursor and the high frequency of tourmaline in the studied sediments may indicate derivation from metasomatized-rich tourmaline source rock.The majority of the encountered grains are zoneless.Zoning, if present, is visible as a faint change in color intensity.Tourmaline grains display a wide range of colors and pleochroism represented by pale yellowish brown, pale green and pink.

Hornblende
The frequency of hornblende is lower in the size fraction 250-125µm than the finer size fraction 125-63µm.It is commonly brown, light green and bluish green to dark green (see Figure 11).It displays diagnostic perfect cleavage that appears imperfect in some cases, depending on the optical orientation of the mounted grains.They are mostly prismatic in shape but occasionally sub-rounded.

Pistachite
It is only detected in the grain size; 125-63µm.This result is similar to the study of the beach sands along the eastern side of the Gulf of Suez, Egypt as quoted by El-Kammar et al., (2007).According to Anfuso et al., (1999), in the coastal sand between Sanlucar de

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ISSN: 2413-5267 Barrameda and Rota, Cadiz, southwest Iberian Peninsula, pistachite accumulates in the finer fraction.In the present study, pistachite is commonly pale yellowish green in color; sometimes it is turbid due to alteration with weak pleochroism and high birefringence as a diagnostic character.

Garnet
According to Anfuso et al., (1999) garnet is more abundant in the coarsest fractions.In the studied samples, it is slightly abundant in the size fraction 250-125µm than in the size fraction 125-63µm.The encountered garnet grains are angular to subangular but occasionally subrounded with characteristic conchoidal fracture (Figure 13).The most common grains are colorless (see Figure 11) but few pinkish grains occur also.In some cases, garnet contains opaque and quartz inclusions.The EDX microanalysis shows that detected garnet is mostly of almandite variety (Table 4).

Monazite
It is pale yellow in color with high relief and very weak birefringence (see Fig. 11).It occurs as rounded grains of spherical and ellipsoid shapes, sometimes with strongly pitted surface.

Rutile
It either occurs as subangular grains or rounded grains (Fig. 14) with a relative preponderance of the former.The yellowish-brown and deep reddish brown colors characterize the encountered rutile (see Fig. 12).It is a well-known fact that rutile can contain highly charged elements (V, Cr, Fe, Al, Nb, Sn, Sb, Ta, W) up to the %-level (Smith and Perseil, 1997;Zack, et al., 2004).The EDX microanalysis shows that the studied rutile is a good accumulator of chromium (Table 5).The rutile composition is not the same in the studied sediments, suggesting derivation from various provenances.

Titanite
The reddish brown titanite is the only detected type (see Figure 11).It is commonly prismatic to sub-rounded grains in shape, occasionally displaying imperfect cleavage.

Augite
Its frequency is slightly lower in the size fraction 250-125µm than in the finer size fraction 125-63µm.It has yellowish brown color (see Figure 11) and exhibits perfect cleavage.

Biotite
It dominates in the 250-125µm size fraction.It belongs to the green variety of biotite (see Figure 11) and seems to be fresh with diagnostic bright yellowish peripheries.Fine inclusions of opaque minerals are sometimes frequent.

Kyanite
It is only detected in the grain size 125-63µm.It occurs as colorless short prismatic subrounded grains with marked right-angled cleavage (see Figure 11).

Opaque minerals
The SEM examination indicates that the detected opaque minerals are mainly magnetite, ilmenite, and goethite (Figure 16).According to Mohapatra et al., (2016), ilmenite is commonly present in the very fine sand fraction.

Sediments Type
Mixes of carbonate and clastic sediments, which are commonly encountered in the Recent coastal sediments, require careful analysis if they are to be correctly interpreted (Carter, 1982).Various methods can identify and quantify the mixing of carbonate and clastic sediments.Mount (1985) pointed out that carbonate sediments incorporate more than 10% terrigenous constituents considered to be of a mixed carbonate-clastic character.On the other hand, varied levels of CaCO3 content propose transition region between the terrigenous and carbonate provinces, commonly ranging from 25 to 75% (Hernandez Arana et al., 2005).In agreement with Gomez-Pujol et al., (2013), the authors believe that cluster analysis can classify the sampled stations (Figure 17) as follows:

Province One (from Bin Jawwad to Ras Al Alas)
The sediments of this province contain mixtures of clastics related to different sedimentary rocks of limestones, evaporites, sandstones and mudrocks, along with green sediments.Mineralogically, in this province quartz and carbonates are present in roughly equal abundances, with feldspars and evaporites contents in the range of 7 to 17% and 6 to 13%, respectively.Medium to high concentration of heavy minerals characterizes also this province.The detected heavy minerals are zircon, tourmaline, pistachite, hornblende, garnet, monazite, rutile, titanite, augite, biotite, and kyanite.

Province Two (from South Ras Al Alas to Shatt Qabis)
The sediments of this province consist of a mixture of clastics derived mostly from sandstones and limestones.Mineralogically, in this province carbonates dominate over quartz, with minor feldspars and evaporites in the range of 0.24 -3%, and 1 -5%, respectively, with a complete absence of titanite and kyanite.

Province Three (from North Shatt Qabis to Benghazi)
Mineralogically, the clastics of this province are carbonate-dominated, with subordinate quartz but very poor in feldspars and evaporites.The heavy minerals in this province are extremely rare.Zircon, tourmaline, monazite, augite, biotite and rutile are the only detected heavy minerals.
Based on the difference in minerals concentration among the three provinces, and considering the geology of the surrounding areas, the authors believe that the studied beach sands in provinces one and two were derived from the sea accumulation (carbonates and evaporates), surrounding carbonate rocks (carbonates), terra-rossa soil and sandstones (quartz, feldspars and heavy minerals).In province three, the sands are derived from the sea accumulation (carbonates and evaporates) and surrounding carbonate rocks (carbonates).The heavy minerals and some light minerals (quartz and feldspars) originated from the aeolian Faculty of Marine Resources, Alasmarya Islamic University, Libya.

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ISSN: 2413-5267 sands related to the widely distributed igneous and metamorphic rocks in many parts of Libya such as Jabal Al Tibisti, Jabal Al Haruj Al Swad, etc.

Conclusions
The present study provides genuine data on the "very fine" and "fine" sand size fractions (125-63μm and 250-125μm) of the beach sands along the Mediterranean Coast from Benghazi to Bin Jawwad, Northeast Libya.These sediments represent a mixture of carbonate and noncarbonate materials at different quotients.The detected light minerals are calcite, aragonite,

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ISSN: 2413-5267 quartz, feldspars, and evaporites, whereas the recorded heavy minerals are zircon, tourmaline, pistachite, hornblende, garnet, monazite, rutile, titanite, augite, biotite, kyanite, chromian spinel, magnetite, ilmenite, and goethite.The heavy minerals in the eastern side are extremely rare, while medium to high concentration of heavy minerals characterizes the sands of the western and central parts.The XRD analysis shows that aragonite dominates over calcite, in the central and eastern sides of the studied beach, whereas calcite dominants over aragonite in the western side, suggesting a difference in sediment age.The central and eastern sides consist of younger sediment, while older, reworked and diagenetically transformed material dominates in the western section.The cluster analysis extracted three distinct groups of sediments.The ZTR index suggests that the studied beach sands are mineralogically submature sediments.

Figure 1 .Figure 2 .
Figure 1.Landsat images showing the location of the study area and the location of the sampled stations

Figure 5 .Figure 6 .
Figure 5. Frequency distribution of the light minerals in the study area (size range: 125-63µm)

Figure 10 .
Figure 10.BSE images showing.a) prismatic crystals of gypsum on Mg-silicate matrix where halite crystals and tiny zircon inclusions are recorded, and b) well cubic halite grain (size: 125-63µm)

Figure 17 .
Figure 17.Dendrogram from cluster analysis (Ward method) of the sampling stations Shaltami et al, 2016Faculty of Marine Resources, Alasmarya Islamic University, Libya.

Table 2 .
Calcite/aragonite ratio on basis of XRD analyses