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Peridot gemstone exploration

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SRK News | Issue 57Exploration Geology: Keys to success

Pengfei Xiao, Geologist/Geophysicis


Exploring for coloured gemstones is different from exploring for other metals or coal; the key to successful exploration is collaboration between gemologist and geologist. In 2017, SRK was commissioned by Yanbian FULI Peridot Mining Industry Co., Ltd to undertake a technical assessment of its Yiqisong Nanshan peridot project in northeast China.

Globally, there are two main types of peridot deposits that are distinguishable on the basis of the host rock: basaltic eruptive and ultramafic intrusive. Most peridot gemstones are the basalt type, while the smaller, ultramafic intrusive type deposits often supply the largest and finest gemstones.

The geological history of the Yiqisong Nanshan deposit includes volcanic eruptive activity and an associated peridot mineralisation event. The peridot is predominantly hosted in ultramafic inclusions within a basalt layer. In rare cases, peridot deposits are found in isolation in the basalt formation. The relationship between the percentage of ultramafic inclusions and the grade of gemstone peridot is well defined at the global scale but is less precise in specific drill core or bulk samples.  

Between 2014 and 2016 exploration activities at the site involved drilling, trenching, and underground bulk sampling. The drilling led to delineating the mineralised zones, which were shown to be relatively shallow-dipping within basaltic layering. The percentage of ultramafic inclusions was calculated from each section of drill core samples.

While the acquisition of drill data is an important component, due to the nature of exploration for coloured gemstones, it also must be correlated with other production data. There may be sections without intercepts of gemstone mineralisation, while other sections have grades in the hundreds of carats. Another reason for exercising caution is the fact that most peridot gemstones are hosted in the ultramafic inclusions, for which drill recovery is poor. After reviewing past exploration and resource evaluation work, SRK’s geologist and associate gemologist proposed a revised program for sample verification and additional exploration.

The revised exploration program focused on gathering additional data for verification, integrating data from the two exploration campaigns to build a database. More importantly, the new exploration program employed additional underground bulk sampling and logging the underground workings for the percentage of ultramafic inclusions. The samples were screened, while over 600 pieces of peridot gemstones were handpicked by skilled technicians. These raw gemstone samples were weighed, classified, polished and certified. The data in each process of statistical significance was recorded.

A preliminary resource evaluation of the Yiqisong Nanshan project indicated that the project, as well as the region, has potential to be an important peridot-producing area.

Pengfei Xiao: pxiao@srk.cn
 

 

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