Abstract
Geopetrological model of diamond-bearing fluid-explosive breccia formations is a well-structured system of the features that are typical of several similar formations in the Cis-Ural and West Ural areas of the Perm Krai. The model reflects a number of basic common factors in these structures’ morphology, their rock composition and the conditions for their formation. Regional and local geological positions featuring diamond-bearing formations as well as the parameters common for their widespread formation areas are characterized. The necessity of mineralogical and geochemical studies of black sand, while prospecting for diamond-bearing targets is highlighted. This will help identify specific mineral associations and geochemical anomalies typical of these widespread formation areas. The description of the geological structure, which the best-studied Efimov deposit, is given in detail. The description of this deposit is used as an example of illustrating the shape of breccia bodies and their polyphase structure, as well as describing their texture and rock structure specifics. Particular attention is paid to the petrographic characteristics of all kinds of fluid-explosive breccias, which to a different extent contain clastic, protomagmatic and newly formed fluidogenic material. The paper gives the characteristics and specifics of mineral grains of various origin, many of which are abundant in gas-liquid inclusions, characterized by block extinction, while quartz possess planar elements. Brought into focus are the differences in the diamond bearing capacity of rocks belonging to different successive evolution phases of fluid breccia formations. The model considered in the paper will make it possible in the course of studies of newly discovered breccia structures with a limited number of parameters to predict their missing features and assessment criteria with respect to possible beneficial mineralization.
Highlights
Геолого-петрологическая модель формирования алмазоносных флюидоэксплозивных брекчиевых образований представляет собой формализованную систему признаков ряда однотипных структур Приуральской и ЗападноУральской зон Пермского края
Geopetrological model of diamond-bearing fluid-explosive breccia formations is a well-structured system of the features that are typical of several similar formations in the Cis-Ural and West Ural areas of the Perm Krai
The description of the geological structure, which the best-studied Efimov deposit, is given in detail. The description of this deposit is used as an example of illustrating the shape of breccia bodies and their polyphase structure, as well as describing their texture and rock structure specifics
Summary
В тектоническом плане исследуемые рудные районы находятся на стыке крупных тектонических структур Урала, Тимана и восточной окраины Восточно-Европейской платформы. Однако спецификой именно флюидогенных брекчий, в частности пород Ефимовского месторождения, является то, что в них, наряду с угловатыми обломками, практически постоянно присутствуют округленные и округлые “обломки”, иногда со скорлуповатой отдельностью. По литературным данным [Жуков и др., 1978; Алмазоносные..., 2011], в протолочных и шлиховых пробах для флюидоэксплозивных образований Ефимовского месторождения выделен довольно широкий спектр протомагматических минералов, однако в шлифах эти минералы встречаются крайне редко и в значительной степени подвержены вторичным изменениям, что крайне усложняет их диагностику. Петрогеохимические признаки рассматриваемых брекчиевых пород не однозначно, но относительно и в зависимости от состава присутствующей в них составляющих магматического происхождения, в том числе протомагматических минералов (флогопита, псевдолейцита, санидина, оливина, пироксенов, щелочных амфиболов, хромшпинелидов и др.), позволяют судить о составе и глубинности первичного источника флюида, порождающего брекчии
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