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Gilsonite (uintaite) is a natural hydrocarbon substance of the class known as asphaltites (see Asphalt), occurring as a coal-like solid which is mined much like other minerals and sold essentially in its native state.

The only commercially important deposits of gilsonite in the world are located in the Iran, in the west of Iran. From a point 6-8 km within Gilane Gharb, the area involved extends westward about 100 km into Ghasreshirin. Gilsonite occurs in veins varying in width from a few centimeters to 6 m. The veins are nearly vertical planes running in a northwest-southeast direction, and extending downward from the surface as much as 600 m. Individual veins are as long as 35 km. Elsewhere in Kermanshah, minor deposits of a gilsonite like material have been reported in Khoramabad and Lorestan province.

Extended geological work in the GLB (Global Leading Bitumen) Gilsonite leaves little doubt that the source material was the tremendous oil shale deposits of the contiguous territory, which is further confirmed by certain similarities in the composition of the hydrocarbons involved, ie, both gilsonite and shale oil have a nitrogen content much higher than petroleum oils in general (see Oil shale).

Classification

Gilsonite is classed as one of the asphaltites, which are natural asphalt like substances, characterized by their high softening points (above 110°C). Glance pitch and grahamite are other members of this group, some properties of which are shown in Table 1 (2). The nonmineral constituents are almost completely soluble in carbon disulfide. Solubilities in aromatic solvents are described in ref. 3.

Properties

The tests applied to gilsonite are in many cases the same as those used for asphalt (qv). Typical properties of commercial-grade gilsonite (GLB LTD Gilsonite) are shown in Table
2. Gilsonite is a natural mineral, not a manufactured product, and is, therefore, subject to certain variations. The liquid distillate from the pyrolysis of solid gilsonite was treated with sulfuric acid to produce a nonreactive hydrocarbon fraction which was classified as paraffinic (5). Evidence for pyridines and quinolones in the distillate was apparently based on odor alone. There are several hydrocarbon fractions from gilsonite distillate with many properties similar to those of fractions from crude petroleum (6). Cycloparaffins (naphthenes) and olefins were identified as hydrocarbon types. Several phenols, pyrroles, and pyridines have been isolated in the pyrolytic distillate from gilsonite (7-8). A heavy yellow oil was obtained from undegraded gilsonite in yields of 4-8% (9). Several aromatic and nonaromatic cuts, the latter predominating, resulted from low pressure distillation and silica gel adsorption of the oil. Substituted naphthalenes were indicated in the aromatic fractions by uv spectra. Destructive distillation of gilsonite gave 12 wt % gases, 55 wt % of a liquid pyrolyzate, and 33 wt % coke.

Porphyrin fractions were isolated from ores of two different veins in yields of 0.03 and 0.004% (eg, deoxyphylloerythreoetioporphyrin) (10). The entire porphyrin content is present as a nickel complex. The presence of porphyrins suggests that gilsonite is of plant origin (see Pyrrole and pyrrole derivatives).

Mining

Methods of mining have included the traditional hand pick, pneumatic picks, blasting, and high pressure (up to 13.8 MPa or 2000 psi) hydraulic cutting. All methods have been used concurrently in different mines with the choice depending upon mine conditions, and elevating and surface handling requirements.

Table I. Properties of Gilsonite, Glance Pitch, and Grahamite

Softening Point, Ring and Ball Method, °C

Specific Gravity at 25°C

Mineral

Streak

Fixed Carbon*
Gilsonite or uintaite
Glance pitch or manjak*
grahamite**

Brown
Black
Black

1.03-1.10
1.10-1.15
1.15-1.20

132-190
132-190
188-329

10-20
20-35
35-55

* By proximate analysis, as for coal.
** When substantially free from mineral matter.