Details of Sinclair Zone Project, page-26

It's worth to have a read even though it's a bit lengthy.

The Cesium story is basically one of simple supply and demand. The demand for Cesium products has been growing at a compound rate of between 6% and 8% per annum for a decade as new applications are discovered.
On the supply side, the world's two dominant mines and the principal sources of supply of Cesium to the global market are effectively depleted or facing uncertain futures. Supply from Cabot Corporation has been restricted to certain clients, therefore overall supply is already decreasing. Without a new large-scale resource, the global industry will struggle to secure the raw materials needed for growth or be subject to a significantly increased cost structure. This could be a reality sooner rather than later.
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Cesium is a soft silvery rare alkali metal with chemical properties similar to the other alkaline metals sodium, potassium, rubidium and lithium. The principal and largest volume use of Cesium is in a compound called Cesium Formate, which has the viscosity of water but is 2.2 times denser. For this reason, it is an ideal specialty fluid used in oil and gas drilling and completion to lubricate drill bits, bring rock cuttings to the surface, to control and inhibit corrosion and to maintain pressure on the formation during drilling of the well. It is approved by environmental authorities as safe to use in ocean and land applications as it is the least toxic to the environment, especially the sea floor and its inhabitants.
Cesium Formate brines help oil and gas companies drill up to 74% faster than competing brines, polymers and muds. Cesium Formate that is returned from a drilling job can be mostly recycled, reconstituted and reused, which is not the case with the majority of other drilling fluids. Cesium Formate is water soluble, thus allowing the chips to be washed onboard the rig and deposited back into the ocean. By comparison, when using other drilling fluids such as barite muds, diesel fuel or polymers, the rock cuttings must be transported ashore and cleaned or buried, which adds time and money to the operation.
Cesium compounds are also used as catalysts for accelerating or moderating other chemical processes such as the manufacture of plastics and coatings. Demand has been growing for Cesium compounds used as reagents in the plastics industry and certain Cesium compounds increase the life and power of alkaline batteries. It plays an important role in assisting the catalytic separation of crude oil into many different hydrocarbon products.
Fission by-products such as the isotopes Cesium131 and Cesium137 are increasingly used to treat various types of cancer. Cesium is not naturally radioactive but it can acquire certain radioactive properties as it used as a very effective heat transfer fluid to cool the operation of nuclear reactors. There are many opportunities to adapt the properties of Cesium Formate in numerous heat transfer applications.
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Cesium also has a range of applications in the production of electricity, and in electronics, as well as chemistry. For example, Cesium carbonate is used in the alkylation of organic compounds and in energy conversion devices such as fuel cells, magneto-hydrodynamic generators, and polymer solar cells. It is widely used in the field of DNA applications.
Cabot Corporations’ Tanco (Tantalum-Lithium-Cesium) mine is an underground deposit located beneath Bernic Lake in Manitoba. Until recently it has supplied ~80% of world demand for Cesium compounds and has essentially been a monopoly producer and supplier of Cesium Formate since 1994. Cabot does not sell Cesium Formate but rather employs a lease- style revenue model. This model makes it virtually impossible to determine how many barrels of Cesium brine are used per year. Estimates of Tanco’s formate production vary but production in 1997 was reported at 500 barrels per month and expanded in 1999 to 700 barrels per month. No cost of production or revenue is available as Tanco is a private Canadian company that is not required to publish its business information in the public domain.
Unfortunately, in 2010 the Tanco Mine suffered a "fall of ground” which was followed in 2013 by a second and larger fall of ground. This is due to the fact that the crown pillar of the mine is undergoing compression, causing unstable ground conditions and allowing lake water to enter the mine. These occurrences have curtailed pollucite production and sterilized parts of the ore bodies. Pollucite is the principal ore mineral of Cesium.
The Manitoba Department of Mines investigated the cause of the ground falls and determined that the mine was unsafe. It requested that Cabot Corporation develop a mitigation plan. The plan that Cabot submitted was not satisfactory, as it required pumping a large volume of organic rich water into the Bernic River which is connected to the Winnipeg fresh water supply. Subsequently, the Department of Mines ordered the mine closed. It is now on care and maintenance, and its future ability to provide Cesium to the global market is unknown. Current production from Bernic Lake is from above ground storage and waste piles.
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The second largest global source of Cesium was the Bikita Mine in Zimbabwe. Bikita was discovered 65 years ago and it has been a producer of lithium minerals and ores and some pollucite for over 50 years. Currently pollucite from Bikita is being produced from above ground stockpiles and waste dumps. The raw material pollucite is shipped from Bikita to Germany and China for processing. Anecdotal evidence suggests there are only two to three years of above ground resources of pollucite in inventory. It is believed that the pollucite zone in the Bikita pegmatite is exhausted. So far there are no new discoveries of pollucite, and no new known mineral that contains Cesium, excepting that at Taron.
Additionally, even if there were legitimate pegmatite exploration targets with potential to host pollucite zones, it may take an enormous exploration effort that could require more than ten years to produce a discovery and many more years to establish production, all of which will cost many millions of dollars. Taron may be as little as two to three years away from production of Cesium Hydroxide.
Historically, Cesium has been extracted from the mineral pollucite and to a lesser amount from lepidolite, as is the case at Tanco and Bikita. Marginal production of pollucite coming from China is hosted in narrow veins and dykes, and volume of supply is constrained. The Chinese deposits are expensive to mine and the processing technology is also expensive. There are over three hundred Lithium-Tantalum-Cesium pegmatites known and catalogued in the world, and several have been drilled. So far only four deposits were large enough and high enough in grade to support the expense of building a mine that could supply the global Cesium market. Two of these are now collector sites for Cesium and other rock specimens.

https://www.cascadero.com/site/assets/files/.../3_3_17taron-website-presentation.pdf