ZABARGAD ISLAND

COMPILED BY..HASNAA Y. SALEM

An introduction to..

•St. John's Island (also known as Zabargad, Zebirget, Topazios) is the largest of a group of islands in Foul Bay, Red Sea in Southern Egypt. •It covers an area of 4.50 square kilometers (approx.). •It is not a quaternary volcanic island, but rather is believed to be an upthrusted part of upper mantle material. •The nearest island is Rocky Island.• The island is slightly north of the Tropic of Cancer, and its highest point is 235 meters.

Zabargad Isand,Egypt

Satellite map of Zabargad Island, Egypt, above

Archaeology of Zabargad IslandResearchers report on peridot mining in the Red SeaSt. John’s Island or Zabargad, the Arabic word for peridot, is purportedly the world’s oldest known source of gem olivine .

Situated in the Red Sea about 45 km. southeast of Ras Banas on the coast of Egypt, much has been written about Zabargad’s unusual geology and modern workings; however, unequivocal evidence of an ancient mine has not been reported until now .

The picture indicates Forsterite ( Olivine )Size: 1.3 x 0.7 x 0.4 cm.A gem peridot crystal from the classic locale for gem forsterite - St. Johns Island in the Red Sea off Egypt. This ancient locality was mined for peridot or "night emerald" as it was called, in the time of the Egyptian pharaohs. This is a locale now long gone and to my knowledge not collected from after the early 1900 s at latest. In fact, the site is now under the Red Sea. This is a superb, historic gem crystal and a fine thumbnail as well.

In an article appearing in the November / December issue of MINERVA magazine (“Egypt’s Evening Emerald,” pp. 16–19) ,

James Harrell (University of Toledo, USA) and Elizabeth Bloxam (Monash University, Australia) provide the first description of the ancient mine .

Ancient writers identified Zabargad as Ophiodes (Snaky) and also Topazos, and they called the yellowish green transparent gem found there topazos.

Peridot appears to have been used sparingly in the Mediterranean cultures of the Hellenistic and Imperial Roman periods .

Extant examples are primarily intaglios or plain, unengraved ringstones and their dates of manufacture range between 250 BCE and 500 CE.

Gem quality peridot specimens, below, from modern and ancient mines on Zabargad Island, collected by James Harrell, 2010; cabochon (12.7 x 9.9 x 3.9 mm.) from modern mine purchased in Cairo market in 2009. (Photo: Lisbet Thoresen)

Specimens of gem quality peridot from the ancient mining site on Zabargad Island. Collected by James Harrell, June 2010. (Photo: Lisbet Thoresen)

Commercial peridot and garnierite mining occurred on Zabargad Island during the first half of the 20th century, but since then the island has been abandoned except for the occasional temporary military camp .

The ancient mine is located on the island’s southeast shore and consists of roughly 150 surface pits, which individually are up to 20 meters across with adjacent spoil piles as high as 5 meters. Peridot crystal fragments up to 1.5 cm across are commonly found on the surface within these workings .

Also associated with the mine are the ruins of stone dwellings, which housed the miners, and a well that provided them with water. Pottery fragments, which are especially common around the well, date mainly from the 3rd to 1st centuries BCE of the Hellenistic period with the rest extending into the Roman period.

Similarly large peridot crystals undoubtedly came from the ancient mine, as well .

The modern mine reportedly yielded whole crystals up to 20 cm in length, and crystal fragments nearly as large as this were observed by the authors

Mining activity on Zabargad probably closely mirrored the rise and fall of Berenike’s fortunes, which peaked in the 1st century CE, and when this city was abandoned by the mid-6th century CE, so also was the peridot mine on Zabargad Island.

The miners and their supplies would have come from the Graeco-Roman port city of Berenike, on the Egyptian mainland 80 km. northwest of Zabargad Island

Zabargad peridotite: Evidence for multistage metasomatism during Red Sea rifting

New analyses of rare earth elements (REEs) and abundances of K, Rb, Sr, Ba, Th, U, Ta, and Hf in peridotites from Zabargad Island, Red Sea, indicate that light REE-enriched amphibole peridotites in the northern and central bodies have undergone a complex, multistage, metasomatic history during Red Sea rifting. The metasomatism is partly attributed to the passage of alkalic basalts through the mantle lithosphere, which possibly occurred during the early, continental-rift history of the Red Sea .

The metasomatism also results from the interaction of the uppermost lithosphere with hydrous crustal fluids released from thinning continental crust. The last metasomatic event is associated with the development of an oceanic hydrothermal system in the Red Sea, after the continental breakup. The available data also suggest that the Zabargad peridotites represent pieces of pan-African lithospheric mantle (the northern and central bodies) pierced by asthenospheric material (the southern body) .

JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 91, NO. B1, P. 599, 1986doi:10.1029/JB091iB01p00599

Exceptionally fresh peridotite bodies outcrop on Zabargad Island, an uplifted fragment of sub-Red Sea lithosphere. The peridotites are associated with basaltic dikes and are in tectonic contact with a metamorphic unit and with post-Mesozoic sedimentary units. The peridotites can be divided into three main groups: (1) protogranular spinel Iherzolites (sp-lherzolites), with average modal composition ol 65%, opx 16%, cpx 16%, spinel 3% (2) amphibole peridotites (amph-peridotites), containing >2% magnesio-hornblende (3) plagioclase peridotites (pl-peridotites), containing >2% Ca-plagioclase.

Peridotites from the Island of Zabargad (St. John), Red Sea: Petrology and geochemistry

Minor outcrops of dunite and wherlite were also observed. The pl-peridotites and amph-peridotites, which are found in localized zones or bands within the sp-lherzolite, show textures ranging from por-phyroclastic to cataclastic, indicating varying degrees of tectonic deformation. Olivine and opx have a rather constant composition in the three groups, Fo ranging between 87.3% and 90.5% and En between 88% and 89%, respectively. Clinopyroxene is chromian diopside but contains less Na in the pl-peridotites than in the sp-lherzolites. Both opx and cpx are moderately Al and Cr-rich, as is typical of mantle-equilibrated pyroxenes .

Spinel has a very low Cr/Al ratio in the sp-lherzolites, lower than in the pi- and amph-peridotites. Plagioclase in the pl-peridotites ranges between An 80% and 93%, while traces of it rimming spinel in some of the sp-lherzolites are more sodic. The amph-peridotites contain up to 28% magnesio-hornblende and, in some cases, traces of phlogopite and apatite; opx, cpx, and spinel are scarce. The major element composition of the Zabargad sp-lherzolites, their slight light rare earth element (LREE)-depleted pattern, transition elements Sc, Ti, Cr, Mn, Fe, Co, and Ni data, together with modal and mineral chemistry data, are all consistent with the sp-lherzolites having last equilibrated in the sp-lherzolite stability field (>9 kbar, >30 km deep) and representing essentially undepleted parental mantle material, though some samples might have undergone minor partial melting

The pl-peridotites may represent localized incor-poration of a melt component by the ascending Iherzolite body. The amph-peridotites are enriched in K, LREE, and occasionally in P relative to sp-lherzolites; they were probably formed by localized contamination with H2O-rich metasomatic fhids injected through the Iherzolite body during its ascent. The Zabargad peridotites were probably emplaced from the upper mantle into the crust during the development of the Red Sea rift, i.e., in post-Mesozoic time

They show affinity with some mantle-derived oceanic ultramafics, particularly with St. Paul Rocks in the Atlantic. They could be considered a sample of oceanic mantle before extraction of the basaltic oceanic crust