The Jabal Ishmas-Wadi Tathlith gold belt is a north-south zone of numerous ancient gold mines in the southeastern Precambrian shield of Saudi Arabia, extending along long 43?30'E. between lat 18?N. and 21?30'N., a distance of about 390 km. The gold belt coincides with a major zone of faulting, shearing, and alteration. The fault zone and most of the gold mines occur within a belt of layered metavolcanic and metavolcaniclastic rocks that is situated between a continuous belt of gneissic rocks to the west and a discontinuous belt of gneissic rocks to the east. Layered rocks are slightly to highly metamorphosed andesitic to dacitic volcanic rocks intercalated with volcaniclastic sediments. Massive volcanic rocks predominate in the southern and very northern parts of the belt whereas medium- to fine-grained sedimentary rocks and volcaniclastic rocks, in part younger than the massive volcanic rocks, predominate in the central portions.
There are five geographic groups of ancient gold mines in the belt, each of which contain deposits that are probably genetically related and are typical of that group. These deposits are hydrothermal in nature and are in or next to quartz veins, quartz breccia zones, or quartz stringer zones. A few of the deposits are spatially related to felsic dikes or small bodies of gabbro but most are in quartz veins of regional systems.
In order to facilitate evaluation of individual deposits, a model was developed to determine the potential resource of each deposit. The model was developed from historical data and utilizes geologic parameters and analyses of waste dump samples to give an optimum potential resource tonnage and grade. Although these are only estimates based upon present exposures and limited analytical data, the results indicate that the deposits in the gold belt have limited economic potential. A majority of the prospects evaluated are small deposits, each estimated to contain less than 50,000 tons of gold ore. Twelve of the prospects are estimated to contain deposits ranging from 50,000 to 400,000 tons of ore at grades ranging from 7 to 32 grams per ton (g/t).