AURIFEROUS QUARTZ VEINS AT ROMIT AREA, SOUTH EASTERN DESERT, EGYPT: GEOLOGIC SETTING AND GEOCHEMICAL SIG-NATURE

Romit area is located in the southern part of Eastern Desert and covered by late Proterozoic igneous and metamorphic rocks. Metavolcanics and tonalite-granodiorites form most of the main outcrops in the area, which is cut off by quartz veins carrying radioactive and rare earth elements, in addition to gold. Major oxides were analyzed using conventional wet chemical analysis, trace element using X-ray ﬂuorescence (XRF), rare earth elements (REE’s) by an Inductively Coupled Plasma Emission Spectrometry (ICP-ES) and U and Th chemically by Arsenazo III. The heavy minerals were investigated by using environmental scanning electron microscope (ESEM) and identiﬁed by X-ray diffraction technique (XRD). Gold concentration was conﬁrmed using ﬁre assay methods (EMRA). This work aims to study the geologic, geochemical and mineralogical characteristics of auriferous uraniferous quartz veins at the Romit area. The discovery of radionuclides and gold mineralization were recorded in quartz veins for the ﬁrst time. The Romit quartz veins have relatively high uranium and thorium contents. The average uranium and thorium contents are 49 ppm and 75 ppm, respectively. The quartz veins of the Romit area show enrichment in some rare metal (Zr, Y, Nb, Pb and Au). The high content in some rare metal in these quartz veins is due to the invading hydrothermal ﬂuids in the later stages of magmatic activity. So, these hydrothermal ﬂuids are potentially important in the dissolution, transportation and precipitation of these elements in these quartz veins. Generally, the rock is characterized by relatively high content of rare earth elements and characterized by negative Eu and Ce anomalies. The identiﬁed minerals in the studied quartz veins can be grouped into U-Th-REE-bearing minerals (kasolite, uranothorite, columbite, monazite, allanite and xenotime), base metal minerals (gold, cerussite, pyrite and arsenopyrite), Oxide minerals (chromite, goethite, rutile and pyrolusite) and silicate minerals (kaolinite and spessartine). Environmental Scan Electron Microscope (ESEM) and ﬁre assay techniques in quartz veins with high contents reach up to more than 1 ppm.

Quartz is the most important silica mineral and widely occurs in igneous, metamorphic, sedimentary and hydrothermal rocks of the Earth's crust.Because of its abundance and properties, quartz finds many applications in industry and scientific researches (Götze, 2012).For instance, its luminescence, geochemical properties and hosting fluid/mineral inclusions have provided critical knowledge for reconstructing geological processes (Burley et al., 1989 andRusk, 2012).In hydrothermal ore deposits, quartz is the most common gangue mineral and may intergrow with metals (such as native gold) and sulfides containing metals such as copper, tin, and tungsten (Pirajno, 2009).
The present work throws light on the geology, mineralogy of the area.It also, focuses on the new occurrence of gold mineralization and geochemistry of rare earth elements (REE) in the quartz veins of Romit area.

GEOLOGICAL SETTING
The rocks in the area are represented by the metavolcanic, tonalite granodiorite, alkali feldspar granite and sandstone.
Moderate to high relief terrain, mainly covered by igneous and metamorphic rocks (Fig. 3), characterizes the study area.Metavolcanics and tonalite-granodiorites form most of the outcrops in the area.Metavocanics are composed mainly of metarhyodacite and metarhyolite.They are fine grained, massive and vary in color from light gray and dark gray to pinkish gray.The weathered surfaces of metavolcanics range in color from greenish gray to pinkish dark gray.They show high luster and break with a concoidal fracture (Fig. 4).These rocks are highly altered, weathered, exfoliated, and composed mainly of quartz, plagioclase, biotite and some muscovite (Fig. 5).Metavolcanics are fragmented and highly dissected by several trends of joints.They are fractured, jointed and characterized by porphyritic textures (Fig. 6).It is common to see hematitic and kaolinitic alterations, especially at fault intersections and along fractures.They are often injected along the extension planes.Field relations reveal that they are intruded by metamorphosed sandstone with sharp contact.This metamorphosed sandstone rock is fine-grained, pinkish white in color, highly sheared, highly jointed and banded.This metamorphosed sandstone is found forming a cap cover the top part in the northern side Several types of dykes cut through the rock parts in the working area where, basic dykes are more abundant than acidic dykes (Fig. 7).All the dykes extend in a NW direction parallel to the trend of the shear zone.The acidic dykes are represented by a rhyodacite and occur in the northern part of the study area.The basic dykes are represented by andesite.The andesite is recorded all over the mine area.Quartz veins are also recorded cutting through all rock units (Fig. 8).The average content of gold in the smoky quartz veins is higher than that of the milky quartz veins.This is probably due to the fact that record of the gold mineralization in the Eastern Desert is commonly associated with smoky quartz (Takla et al, 1995).

SAMPLING AND METHODOLOGY
Six samples were collected from the quartz veins of Romit area and subjected to mineralogical studies and chemical analyses.For the mineralogical investigations, heavy liquids separation technique was used to concentrate the heavy minerals.The heavy minerals were picked under binocular microscope and investigated by using environmental scanning elec- Determination of U and Th chemically was carried out by Arsenazo III using spectrophotometer model Prolabo, Jean and constant U.V. The major oxides are analyzed using conventional wet chemical techniques of Shapiro and Brannock (1962).Trace element concentrations were determined using an X-ray fluorescence (XRF) spectrometer from PHILIPS, model X'Unique-II.Rare earth elements (REE's) are measured using an Inductively Coupled Plasma Emission Spectrometry (ICP-ES).The Egyptian Nuclear Materials Authority's labs performed all the aforementioned tests (NMA).
For measuring gold concentrations, fire assay analyses were carried out at the Egyptian Mineral Resources Authority (EMRA), Central Laboratory Sector.Weigh 50 g of the sample, addition of flux (litharge -borax -sodium carbonate -flour -silica -silver), mixing the sample with flux in a ceramic crucible, melting of (sample + flux) at 1000° C for 1.5 hours, cupellation of (lead + gold +silver) alloy at 900°C for 1 hour, parting of resulting (gold -silver) alloy in nitric acid and aqua regia heating to get gold solution, and finally, analysis of gold solution by GBC Avanta atomic absorption instrument to get gold concentration with ppm.

MINERALOGICAL STUDIES
The studied mineralization of Romit area can be classified into the following groups: (1) U-Th-REE-bearing minerals (2) Base metal minerals (3) Oxide minerals (4) Silicate minerals

U-Th-REE-Bearing Minerals
Kasolite [Pb(UO 2 )SiO 4 .H 2 O] is generally distinguished from the other uranium silicates by its crystal habit and luster.It is present as yellow crystallites (Fig. 9) with resinous luster.The X-ray diffraction analysis detected the presence of kasolite mineral (Fig. 9).The EDAX analysis data refer to presence of 52.93% U, 39.29% Pb and 5.66% Si with traces of Fe and K (Fig. 10).
Uranothorite (Th,U)SiO 4 ), has dark brown and brownish to pale-brownish colour (Fig. 11).The uranothorite was determined by X-ray diffraction (Fig. 11).From the EDX data, uranothorite contains an average 51.34%Th and 9.57% U (Fig. 12), it contains considerable amounts of Pb, Ca and Mn but it is almost free of any REE.
Allanite [(Ce,Ca,Y,La) (Al,Fe +3 ) 3 (SiO 4 ) 3 .OH], is one of epidote group which can incorporate significant amounts of U, Th and LREE.The presence of the most radioactive elements in most cases led to breakdown of its crystal structure and allanite inverted into amorphous substance due to the radioactive emanations (Keer, 1959).From the EDX data allanite contains an average 35.09%Ce, 14.89% La, 10.13% Nd, 3.53% Pr, 1.47% Sm, 2.76% Gd and considerable amounts of Ca, Fe, Al, S and Si (Fig. 17).
Xenotime (YPO 4 ), exhibits translucent yellowish red to reddish brown colors (   AURIFEROUS QUARTZ VEINS AT ROMIT AREA, SOUTH EASTERN and extensive sulphide mineral.It is occurs in many hydrothermal vein deposits over a wide range in temperatures.Its color is yellowish gray to gray with metallic luster.It is identified by X-ray diffraction associated with arsenopyrite (Fig. 20).ESEM analysis shows that pyrite contains 43.55% Fe, 51.33% S (Fig. 20).
Arsenopyrite (FeAsS), occurs as steel gray to silver white crystals (Fig. 21).Large levels of gold may be found in association with arsenopyrite.As a result, it can be used as a marker for reefs that actually contain gold.Arsenopyrite occurs in hydrothermal veins and zones of contact metamorphism or metasomatism where temperatures are high.The X-ray diffraction analysis detected the presence of arsenopyrite mineral associated with pyrite (Fig. 21).The EDAX analysis data refer to presence of 34.55% Fe, 44.86%As and 20.59% S (Fig. 22).
Cerussite (PbCO 3 ), is a mineral for lead and is a public alteration product of galena and occurs as yellowish color with sub-rounded form.EDAX analysis data show that cerussite have 88.11%Pb (Fig. 23).
Monazite (Ce,La)PO 4 is a chief rare earth-bearing phosphate mineral occurring as accessory mineral.Monazite crystals occur as brown to reddish brown prismatic or tabular habit.Lazareva (2018) concluded that the monazite structure would accept REE ions radii between those of La and Eu.Based on the existence of a solid -solution series between (Ce, La) PO 4 and Ca Th (PO 4 ), the structure will accommodate ions with radii between those of Ce and Ca.EDX analysis revealed the presence of monazite (Fig. 18).

Base Metal Minerals
Gold (Au), it one of the rarest metals in the earth's crust with an average grade of only 0.002 ppm Au.In comparison, silver average 0.08 parts per million (ppm) and platinum average 0.01 ppm (ppm) in the earth's crust.Gold's rarity and bright color have long attracted humans, and objects created from the precious metal have been documented as far back as 5,000 B.C.It is a yellow precious metal and analyzed by ESEM technique contains 68.29% Au in selected spot and found associated with As and Cl (Fig. 19).
Pyrite (FeS), represent the most rich     Rutile (TiO 2 ), is a major mineral source of the titanium, it typically includes about 60% titanium and 40% oxygen.It can have some iron, sometimes up to 10%.It is euhedral to subhedral elongated grains with brown red colour and rode-like crystal habit (Fig. 27).Ru-

Oxide Minerals
Chromite (FeCr 2 O 4 ), is commonly located in the rocks in the studied area.Chromite appears as massive grains of black to brownish black color and has metallic luster.The SEM data of chromite shows its main constituents as 74.28%Fe and 10.86% Cr (Fig. 24).Goethite (FeO.OH), is formed by the oxidation and hydration of iron minerals or as a direct precipitate.Pyrolusite (MnO 2 ), represents one of the most commonly manganese minerals, formed under highly oxidizing conditions in the oxidized zone of ore deposits.Mn-oxides may also be displayed as dendrites on fracture surfaces of rocks with grey or black color.EDAX analysis data show that pyrolusite have 71.73%Mn with minor Pb, Fe, K, Si, Al and Ca (Fig. 29).

Silicate Minerals
Kaolinite [Al 2 Si 2 O 5 (OH) 4 ], is an import-ant hydrothermal mineral and occurs abundantly in hydrothermal rocks.The process of hydrothermal alteration is responsible for its formation and weathering of intermediate basic and acidic rocks.It is appear as complex crystals associate with quartz grains (Fig. 30).The XRD diffractogram (Fig. 30) shows the presence of kaolinite associating quartz.EDX analyses show that kaolinite have 43.13%Al and 41.88% Si (Fig. 31).
Spessartine [Mn 3 Al 2 (SiO 4 ) 3 ], represents one of the garnet groups which are closely related minerals.The color of garnets is extremely variable but is mainly controlled by the amount of Fe, Mn and Cr present ( al., 1992).Spessartine mineral is represented by dark orange color (Fig. 32), vitreous luster and white streak.The X-ray diffraction analysis recorded spessartine mineral (Figs. 32).Sub-angular to sub-rounded spessartine mineral 33.39% Al, 47.57% Si, 3.04% Mn by ESEM (Fig. 33).

GEOCHEMICAL AND RADIOMETRIC ANALYSIS
The quartz veins samples of Romit area were analyzed quantitatively for U, Th, major constituents and trace elements (Table 1).

RARE EARTH ELEMENTS
The mean abundances of rare earth elements, and the shape and slope of chondritenormalized REE patterns, are distinctive for quartz samples.It is impossible for REE to act as isomorphism exit in quartz crystal because the ionic radius of most of REE is far longer than that of Si (Mu, 1999).The REE in quartz are mainly concentrated in fluid inclusion.The REE in fluid had not been impacted by quartz crystal that cannot be shaped by REE in its hydrothermal metasomatism and precipitation process.REE of quartz which are analyzed represent the REE in hydrothermal fluid.As a good geochemical tracer, changes in REE characteristics are often interpreted as changes in the source of fluid (Li et al., 2003).
Generally, the rock is characterized by relatively high content of rare earth elements with average 114.51 ppm that are attributed to the presence of the REE-bearing accessory minerals as proved by EDX analyses as monazite, allanite and xenotime minerals.The chondrite-normalized REEs pattern (Boynton, 1984) is characterized by negative Eu and Ce anomalies (Fig. 35) with enrichment trend from LREEs (61.45 ppm) to HREEs (53.06 ppm), (Table2).
Eu as an oxidation sensitive element among REE, and is strongly dependent on temperature of depositional conditions (Dill, 2016(Dill, , 2017)).In fact, at temperatures > 200°C Eu 3+ is reduced to mobile Eu 2+ .Therefore, reduced Eu (Eu 2+) preferentially remains in solutions and causes negative anomaly in chemical/biochemical precipitates.In contrast, in low-temperature environments the immobile Eu 3+ prevails and concentrates in chemical/biochemical carbonate precipitates, hence displaying positive Eu anomalies.The studied samples have negative Eu anomaly, reflecting reducing conditions in the depositional environment.Fig. 35: Chondrite-normalized REE's (Boynton, 1984) of the quartz veins.
Under the condition of higher oxygen fugacity, Ce 3+ can oxidize more easily to Ce 4+ valence, which tends to remain in hydrothermal fluid resulting in positive Ce anomaly.Therefore, quartz with negtive Ce anomaly and its being weak or strong are related to redox conditions of the fluid of quartz crystallization (Li et al., 2003;Mu, 1999).The oxygen fugacity was recorded in the quartz samples in their growth environment by negative Ce anomaly.Ce/Ce* and Eu/Eu* minimum in quartz samples which indicates that gold was precipitated in the sudden transformation from strong oxidized conditions to reduced conditions (Li et al., 1996).Kawabe (1995) stated that the 'tetrad effect', 'double-double effect', or 'zigzag effect' are a characteristic feature of REE normalized patterns and could be used to exhibit the geochemical processes.The quantification of the tetrad effects shows the presence of M-type (convex) first tetrad (T1) in sample R6 while W-type (concave) in the third and fourth tetrad (T3 and T4) in the rest samples (Table2).Unusual M-and W-type shape in the normalized REE pattern may clarify the role of hydrothermal alteration, in addition to water-rich solutions in the radioactive and gold mineralization (Abedini et al. 2018;Abed et al. 2022).This may be related to drastic changes in physico-chemical conditions at these rocks.
The ratio La N /Yb N is considered by Rollinson (1994) as a measure of the degree of fractionation of REEs in the melt.Calculation of this ratio for the rock under consideration showed that the REEs are fractionated with low degrees (average 0.50, Table2) indicating that they are slightly fractionated in the melt and highly fractionated in the accessory minerals.Plotting of the same ratio versus Ce N showed positive relation referring to increasing of the degree of fractionation with increasing of the LREE represented by Ce (Fig. 36).
Plotting of Th versus Ce/Th ratio (Fig. 37) and U versus Ce/U (Fig. 38 The variation between U with Th/U ratios shows negative correlation (Fig. 40 and 41) this suggests that the distribution of radioactive elements is not only magmatic but also due to hydrothermal activity.Also, the Th/U value of the studied rocks reflects the oxidation-reduction features of the geological environment (Jones and Manning, 1994): (1) the Th/U value of the oxidizing environment is less than 0.75; (2) Th/U=0.75-1.25 represents relations indicating that the radioelements are not hosted only in the accessory minerals but tend to form their own minerals.
The U and Th contents have average of 49 ppm and 75 ppm, respectively (Table 1).The concentrations of U and Th in the individual mineralized samples are primarily depending on the abundances of U-and Th-bearing minerals such as kasolite and uranothorite.The strong positive correlation between U and Th (Fig. 39), indicated that these two elements are connected together in the mineralization On the light of the presence of gold detected during the mineralogical and SEM techniques in quartz veins samples.This result led to analysis of bulk samples of them using fire assay technique at the Central Laboratories of the Egyptian Mineral Resources Authority (EMRA).The gold content ranges between 0.24 and 1.02 ppm with an average of 0.49 (Table 1).

THE GENESIS OF MINERALIZATION
The mineralogical studies confirm the presence of two mineralization stages, the earliest mineralization stage (high temperature stage) which is characterized by the formation of native Au associated with primary sulfide minerals such as pyrite and arsenopyrite.The high temperature stage was followed by a second lower-temperature stage characterized by the formation of secondary minerals; goethite and kaolinite.
The recorded gold contents in Romit area, considered as first record.The quartz veins samples have higher content of gold (ranges from 0.24 to 1.02 g/t).The occurrence of gold mainly depends on temperature, pressure, pH values, Cl¯ concentration and fugacity of H 2 S in a hydrothermal system.Gold mostly occurs as AuCl 2 in a system with temperature higher than 400ºC (Gammons and Williams-Jones, 1997), and with decreasing temperature being the primary mechanism causing gold deposition.Au(HS) ¯2 is the dominant phase at lower temperature with the decline of oxygen fugacity, the Au-S complex breaks down, leading to gold precipitation (Cooke and Simmons, 2000;Robb,2005 The rare metals enrichment in the study area are formed due to the subsequent processes; including the ascending hydrothermal solution, with further contribution of the descending acidic meteoric water; supergene enrichment processes.The alkaline hydrothermal solution in quartz veins was under pH more than 7 and T. (300ºC to 350ºC).The acidic solution was under pH ranges from 2 to 3 with low temperature varying between 200ºC to 250ºC (Helgeson, 1969).
Precipitation of goethite is due to extensive alteration of pyrite and probably decreased the pH of the alkaline solution and rising acidic fluids.The presence of clay minerals indicates a high temperature environment (higher than 200ºC).The mixing of volatile fluids with meteoric water and fluid-wall rock interaction result in changes in pH and oxygen activity and deposition of hypogene rare metals (gold) and supergene ones (goethite, kaolinite and secondary uranium) filling fractures.
The sudden change in the pH and temperature of the fluids will lead to destabilization of rare metal complexes favoring their deposition (Alexandrov et al., 1985).The rare metals mineralization are accumulate in the residual melt of the late fractionate (Bright, 1974) especially upward in the magmatic system (Smith, 1979).
Depending on Oxygen fugacity (ƒO 2 ) in the final magmatic fractionation, uranium tend to form the relatively soluble uranyle ion (UO 2 ) +2 , hence, hydrothermal processes during final stages of crystallization of magma are important in controlling the later redistribution of uranium within the rocks (O'Connor et al., 1982).The origin of uranium appears to be closely associated with the rare metals mineralization and may be reflects readily their intimate coherence.REE mobility is favored by: low pH, high water rock ratios and abundant complexing ions (CO 3 2-, F -, Cl -, PO 4 3-, and SO 4 2-) in the hydrothermal solutions (Michard, 1989 andLottermoser, 1992).
The REE in Romit quartz veins were brought by hydrothermal fluids into rocks during alteration and may be precipitated such as monazite and allanite.

CONCLUSIONS
Romit area lies at Gabal Ti Keferiai which is located in the southern extremely of the Eastern Desert of Egypt near the Sudan frontier between Latitudes 22 ° 14 ′ 29 " and 22 ° 28 ′ 25 " N and Longitudes 35 ° 34 ′ 21 " and 36 ° 01 " 09 " E. Metavolcanics and tonalite-granodiorites form most of the outcrops in the area which are cutting by Quartz veins.
The quartz veins have a strong enrichment in some rare metal (which Zr, Y, Nb, Pb and Au).Quartz veins show an average result of fire assay of gold is 0.49 ppm.Chondrite normalized REE diagram shows that the quartz veins have enrichment of ∑REE with low degree of fractionation in the melt (0.50) and in turn, high degree of fractionation in the accessory minerals and displays progressive enrichment in LREE relative to HREE.The enrichment of REE may be attributed to the presence of monazite and allanite as a source of LREE and xenotime and garnet as a source for HREE.
The quartz veins show slightly high level of radioactivity giving U average content of 49 ppm while, Th average content is 75 ppm.The present study proved that radioactive minerals responsible for U and Th in the studied quartz veins are kasolite and uranothorite.The Th/U values reflect the reducibility of the ore-forming fluids, coincident with the sulphide minerals (pyrite, arsenopyrite) which indication of gold.
It may be concluded that the hydrothermal fluids responsible for the formation of the studied silica veins and the deposition of Au and U mineralizations in these veins, suffered different physicochemical changes allowing transportation and the associated deposition of Au and U together with sulphides in the study silica veins.

Fig. 20 :
Fig.20: ESEM image and EDX analysis data of pyrite

Fig. 23 :
Fig.23: ESEM image and EDX analysis data of cerussite The spider-diagram (Fig.34) of the trace elements contents of the studied quartz veins normalized to the primitive mantle data (McDonough and Sun 1995) display enrichment of Rb, U, Th, Zr, Nb, Pb and Y and depletion Ba and Sr.These enrichement and depletion of the compatible elements in the examined quartz veins are due to the effects of assimilation of crustal materials.

Fig. 36 :
Fig.36: Degree of fractionation vs Ce N of the quartz veins Fig. 39 : U-Th ratio of the quartz veins

Table 1 :
Chemical analyses of major oxides (wt%) and trace elements (ppm) for the quartz veins of Romit area

Table 2 :
) exhibit negative Chemical analyses of rare earth elements (ppm) for the quartz vein of Romit area processes and mainly incorporated in uranothorite.