Summary:
Jordan is situated on the northwestern side of the Arabian Plate, along the eastern flank of the ancient Tethys Ocean on the western side of the Dead Sea Transform. The country hosts huge phosphate deposits. The deposits at Eshidiya are comprised of overburden, four phosphate beds (A0, Al, A2 and A3), a coquina/marl waste bed, and two silicified phosphate chert interwaste beds.
The Eshidiya phosphate deposits in central Jordan lie within the Upper Cretaceous limestone plateau. They comprise about 125 sq. km and are estimated to be 65 million years old (Upper Cretaceous). The deposits are sedimentary in nature and are thought to have been formed in the following sequence:
(i) upwelling of cold, phosphate-rich seawater into warm shallow waters,
(ii) growth of algae, plants, fish, and mammals due to the rich nutrients,
(iii) phosphatization of calcareous, siliceous and clay sediments on the shallow sea floor, along with deposition of phosphate-rich teeth and bones from animals,
(iv) reworking of the phosphate sediments by current or wave action and finally,
(v) after the seawater receded, weathering of the phosphate sediments, with rains that leached the softer limestone and left behind the quartz and less soluble phosphates.
The phosphorites of Jordan are present within Al-Hisa Phosphorite Formation (AHP). In general, the AHP consists of phosphorites, bedded chert, limestones, oyster buildups, organic-rich marl (oil shale) and other rock types.
The AHP consists of three formal members, from older to younger Sulatani, Bahiyya and Qatrana. In central Jordan, the Sultani Member consists of alternating limestones, bedded chert and minor phosphorites. The Bahiyya Member consists of oyster banks or buildups up 30 m in thickness that are made of oyster fragment in clinoforms dipping general to the SE (Abed and Sadaqah, 1998). The Qatrana Member is the host of the high grade phosphorites. The grade phosphorites are friable with little calcareous cement. They are present as lenses (small basins) with a diameter ranging up to few kilometers and a thickness up 13 m.
In Eshidiyya Basin, the three formal members are present only in the northern parts of the basin. The Bahiyya coquina thins gradually towards the SE until it disappears completely. The Sultani Member or the lower member is hosting the main (high) grade phosphorite deposits. It is divided by the miners into three producing phosphate horizons from top to bottom; A1, A2 and A3, separated by non phosphorite strata like; chert, porcelanite, and minor beds of marl, limestone and dolomite. (Sofremines, 1987; Abed et al., 2007). The A3, at the base, is rich in quartz sand, while A2 is a friable, high grade phosphorite. The A1 is a low grade indurated by calcite cement. The Qatrana Member or the upper member is designated A0 and consists of up to 3 m of friable high grade phosphorite in the north thinning to the SE to few centimeters only.
In sedimentary deposits such as those found in Jordan, the ore generally consists of phosphate particles ranging from 20 mm to 50 microns in size, sand and clay ranging from one mm to less than two microns. Clay can be present in large lumps, but scrubbing and wetting with water will generally reduce it to its natural grain size of less than two microns. The ore beds generally rest on hard limestone and are overlain by overburden sand.
The composition of the studied phosphate is made up of four types of phosphate particles as follows: pellets, intraclasts, skeletal fragments and coated grains. The phosphate particles occurring in the form of subrounded to subangular grains or pellets ranging in size from 0.2 to 0.5 mm. The matrix is mostly calcitic and locally silicic. The main diagenetic replacement of phosphate particles are calcitization and silicification. Francolite is the main phosphatic mineral identified by XRD, whereas calcite, quartz and dolomite are minor elements.