A question was asked to me by a friend that ELM's Congo potash...

A question was asked to me by a friend that ELM's Congo potash deposit is not good because the potash layers are sandwiched between halite layers in Kola.

I think my friend was misinformed by someone or something that he was told the potash layers would be flooded by water during underground mining because the halite layers on the roof are made of salt and easily soluable by water.

That is totally wrong.

Look what the technical potash studies of Saskatchewan says: (ref and link below); "...A minimum salt-back thickness the halite interval directly above the potash member) is required to build a stable solid roof for mining operations. ( Btw, 9 out of 11 potash mines in Saskatchewan are underground mines)

Now, the known best potash deposits (I would like to say "before Congo deposits are explored by ELM", but it would be a bit early) are in Saskatchewan and they are all sandwiched by halite layers.

See this source: Link: Click here and see what PotashCorp says;

"The potash zones are sandwiched between rock salt formations within the prairie evaporite. The lower esterhazy member is mined for potash. The primary lithology is halite with variable amounts of sylvite, carnallite and clay. The main ore zone occurs at a depth of approximately 960m... Rocanville uses a long room-and-pillar method of mining. Ore is mined from rooms in three passes, separated by pillars supporting the overlying strata."

You can see on the graphics below that ELM's Kola deposit is very similar to the deposits in Saskatchewan. They look very similar as they are both Marine evaporites (see Vikipedia;Evaporite). The potash ores are all sandwiched between halite layers. This is because how the potash layers geologically formed in marine evaporition sequences.

In Saskatchewan there are three layers of potash, (in descending order)1)Patience lake 2) Belle Plain 3) Esterhazy. The Esterhazy member is deepest but contains higher grade of KCl.

Why is the halite layer (salt-back) a must for potash mining?
Here it is;

Source:The Stratigraphic Framework of the Potash-rich Members of the Middle Devonian Upper Prairie Evaporite Formation, Saskatchewan
Link: Click here (Attention: this is a 11.5mb pdf file)

"...A minimum salt-back thickness the halite interval directly above the potash member) is required to build a stable solid roof for mining operations. In this study, the thickness, burial depth, and salt-back thickness of the potash members are mapped for the province of Saskatchewan.."(Page 2, paragraph 3)

"The Esterhazy member is the lowermost potash-rich interval of the Prairie Evapotite Fromation ans consist of several potash-rich beds with interbeds of halite and clay seams... The Esterhazy member is mined by conventional underground techniques at the Estherhazy and Rocanville potash mines (of PotashCorp) and bu solution mining techniques at Belle Plaine mine (Mosaic)" (page 6, pharagraph 1)


Source: BHP Jensen project Proposal
Link: Click here (Attention: this is a 105mb pdf file)

Salt Back Thickness (Halite above potash layer).
"The salt back thickness is the thickness between the base of the Dawson Bay /Second Red Beds (at the top of the Prairie Evaporite formation) and the top of the mining cut. The salt back acts as a stable solid roof for mining operations. The widely used and generally accepted minimum salt back in the industry is 10 m, and this value was used for estimating the Jansen Project
resource."
ELMs Sintoukola Potash Project Cross Section




Saskatchewan / Canada Potash members Cross Section
Source:Link: Click here (Attention: this is a 13mb pdf file)
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