The volcanogenic massive-sulfide (VMS) type is one of the major metal resources of the Kingdom. The deposits include Cu, Zn, Pb, Ag, Au mineralization deposited on, or next to, submarine volcanic centers of oceanic-island-arc or back-arc affinity. Generally, they include mafic to felsic volcanic rocks with tholeiitic to calc-alkaline affinities. In Saudi Arabia, most of the VMS occurrences are related to intermediate to felsic rocks, known as the "Kuroko" type. Very few VMS occurrences are chalcopyrite-dominant in basaltic rocks, i.e. the "Cyprus" type. Locally, banded-iron jaspilite associated with felsic volcanics occurs as a sub-economic iron ore of the "Algoma" type.

Nine major VMS belts have been distinguished from south to north:

1) The Tathlith-Najran belt includes more than fifteen base-metal sulfide occurrences of the VMS type, with two potentially economic deposits at Al Massane (Cu, Zn, Au) and Kutam (Cu, Zn). In the eastern part of this belt, some Ni-rich gossans are related to disseminated to sub-massive graphitic-schist-hosted pyrite, pyrrhotite and pentlandite bodies, and are better classified as sedimentary type .

2) The Wadi Bidah - Wadi Shwas belt hosts over sixteen polymetallic VMS occurrences; two are of economic size: Al Hajar (supergene gold) and Jadmah.

3) The Khurmah - Al Muwayh belt includes four occurrences, two of which (Al Gharif and Ar Rjum) are of the sub-aerial epithermal type with a characteristic Ag-Ba-Mn association.

4) The Zalim - Afif - As Safra - Nuqrah belt follows the main Nabitah suture zone. It includes more than 45 occurrences of which about half are pyritic gossans with low precious- or base-metal contents. Nuqrah is a sedimentary/exhalative-rock (Sedex) gold and base-metals deposit.

5) The Samran - Jabal Sayid belt follows the Bir Umq suture zone and contains eight known VMS occurrences, including the major Jabal Sayid (Cu, Zn) deposit.

6) The Al Amar - Khnaiguyah belt (Ar Rayn terrane) hosts seven polymetallic VMS occurrences, Khnaiguyah (Zn) and Al Amar (Au, Zn) being economic deposits. Al Amar probably belongs to the epithermal subtype as exhalative Zn-Cu mineralization is known in the vicinity.

7) The Hulayfah - Hanakiyah belt may be considered as a northern extension of the Zalim belt.

8) The Khaybar - Al Ula belt (Yanbu suture zone) encloses five VMS Cu-Zn showings.

The most northerly Wadi Sawawin belt is clearly distinguished from the others by its Fe-oxide-jaspilite association (Algoma type). From the seventeen described occurrences, only the eight of West Shinfa/Sahaloola may hold economic prospects.

These commodities, i.e. chromium, titanium, iron, nickel, copper, and (minor) platinum-group elements, are related to two main subtypes according to the host rock:

The ophiolitic type: this includes disseminated Cu, Ni and Cr mineralizations in the ultramafic part of such oceanic rocks, or in their serpentinite equivalent. They are found in the various suture zones of Al Ays, Jabal Ess, and Bir Tuluha.

The layered mafic-ultramafic type: this includes the Wadi Kamal complex in the Yanbu suture zone and mafic-ultramafic zoned intrusives of Jabal Rugaan, Lakathah and Jabal Idsas,

None of the occurrences found in rocks of these two types are of present economic interest, but significant PGE wadi sediment anomalies discovered in the Wadi Kamal complex warant a control.

Most tin and tungsten mineralizations are related to highly differentiated granites enriched in volatiles (F, P, Li).

Two subtypes are found in the Shield. They are the Bir Tawilah W-Sb-Bi-Mo mineralization in veins around granite cupolas, and the Silsilah Sn-F mineralization related to greisen alteration within a peraluminous granite intruding Murdama metasedimentary rocks. None of these occurrences is economic at present.

Some younger intrusives are sodic-alkalic granites enriched in high-field-strength elements (Ti, Y, Zr, Nb, Hf, Ta). Some are enriched in niobium, uranium, yttrium. thorium and rare-earth elements (REE), like the Ghurrayah prospect, and others are enriched in heavy REE (Nb, Zr, Y). None of these occurrences is economic at present.

Porphyry-type occurrences have only recently been recognized in the Shield. Commonly, the associated potassic intrusives are spatially associated with quartz ring-veins or aplitic ring-dikes. A common geochemical zonation has Cu-Mo anomalies in the core, Sn-W anomalies near the contact, and Pb-Zn-Ag-Au quartz veins farther out in the country rock. They are found in an inter-arc (microplate) crustal setting, or in younger sedimentary basins such as those of the Murdama and Jibalah.

These occurrences are clustered in eight major districts. These are the Fawarah Murdama basin, the Baid ad Jimalah – Umm Hadid belt, the Ar Ruwaydah belt (west of Al Amar), the Wadi Salamah – Al Khushaymaiyah Murdama basin, the South Afif terrane, the Ghurayrah block north of Khamis Mushayt, the Musayna’ah district (Cu-Au) west of Nuqrah, and the Al Ula -Khaybar district.

Epithermal deposits are commonly associated with (sub-aerial) volcanic rocks that form the upper part of sub-volcanic potassic intrusives in a subduction-related arc setting. However, several epithermal deposits have recently been described from submarine andesitic-rhyolitic volcanoes, e.g., in the fore-arc basin of New Guinea.

The two major gold deposits of the Shield, Al Amar and Mahd adh Dhahab. are related to this type. The Umm Hadid silver occurrence and some Mn-Ba-Ag occurrences may belong to the same group.

More than 700 vein-gold occurrences are reported in the MODS system and several gold districts can be delineated. Most veins are related either to shear zones or to secondary extensional flat dipping thrusts.

The shear zones are major brittle-to-ductile sinistral strike-slip Najd features that transect the Shield; examples are the Halaban - Zarghat fault zone, the Ranyah (Ar Rawdah – Ad Dafinah fault, or the Al Wajh - Hamalyiah fault). Younger post-Murdama intrusive stocks, e.g., the Raha– Ali NaJadl - Mibari district, the Sukhaybarat – Al Jurdhawiyah district, or the Bulgah – As Shumta district, crosscut the secondary thrusts.

Some North-South pre Najd (so-called suture) faults, the Al Amar - Nabitah and Bir Umq sutures, are also associated with gold occurrences. These linear, sheared serpentinite belts, intruded by syn- or late tectonic diorite and granodiorite, were favorable for the precipitation of gold, as at Ghadarah and Hamdah. Pyrite, arsenopyrite, and sericite or chlorite and carbonate alteration are common in these shear zones where they are related to intrusive bodies.

The Sukhaybarat mine (21 t of gold, but nearly exhausted) belongs to this type, as does the Zalim deposit, which holds good economic potential, and Bulgah, Hamdah, and Ash Shakhtaliyah.

During the Late Proterozoic, detrital material and graphitic shale with dolomite and locally barite, were deposited in a near-shore environment within inter-arc basins. Distal epiclastic-volcanic layers indicate volcanic activity along the basin margins.

Several disseminated Pb-Zn (Au-Ag) occurrences are related to this type, e.g. in the Ar Rjum – Al Gharif basin, the As Siham - Shaib Lamisah basin and the Ash Sha’ib basin. Stratabound copper in detrital rock has been recorded from the Ablah graben.

In the southeastern Asir Mountains, several Ni-Mo gossans are related to black shale enriched in pyrite, pyrrhotite and pentlandite. Though at present no occurrences of economic interest are known, the Farah Garan - Wadi Qatan belt could host this type of mineralization.

Along the Red Sea coast, Pb-Zn (Cu) mineralizations are related to Tertiary detrital infilling of (half) grabens, which themselves were created by the tectonic activity accompanying the formation of this new ocean basin. The mineralization is a combination of red-bed type in detrital sediments, and younger Pb-Zn mineralization in Miocene calcareous-reef-related rocks, e.g., the Jabal Dhaylan prospect that belongs to a sub-type mixing unconformity features and hydrothermal activity.

Other Pb-Zn occurrences were discovered during oil-exploration drilling in the Paleozoic and Mesozoic Cover Rocks. Some of them are connected with salt-dome structures of Early Cambrian and Early Jurassic age.

Some marine titanium-rich beach-sand placers were recognized in the coastal plain along the Red Sea shore. However, grades and tonnages are too small to warrant further work.

Gold placers have been explored downstream from certain large ancient gold workings, such as those in the Mahd adh Dhahab area. Although some "colors" were found during panning, the grades are not economic.

Exploration for tungsten (scheelite) and gold in the Quaternary terraces of alluvial piedmont deposits at the mouth of Wadi Unaybik, north of Al Wajh on the Red Sea coast, indicated low concentrations of these metals.