Why is the price of pink diamonds rising?

The Argyle Diamond Mine, which is Rio Tinto's leading mine in Australia, produced last year 14.07 million carats of diamonds. This is a decrease of 18% compared to its production in the year 2017. The decrease in the production of the Argyle Diamond Mine derives from alluvial mining, which is a method of mining the concentrates on collecting the diamonds from the surface of the ground, and it is the most traditional, as well as the most ancient method in world for mining diamonds.
In this method of mining millions of tons of sand, which includes gravel, are disposed of and transferred to a sorting-out and separation. This method is relatively easy, but it requires a lot of patience, and it spreads over vast areas. Therefore, you need heavy machinery and expensive means in order to perform this method.
Argyle, the Australian diamond mine, which is owned by Rio Tinto, is the largest diamond mine in the world in terms of its volume, and it is probably the most famous diamond mine in the world because of the rare pink and red diamonds that it constantly produces since it began to operate commercially in 1983.
Now the famous mine is nearing the end of its activity, and it is expected to be closed during 2020.
The Argyle Diamond Mine is the source for about 90% of the pink diamonds in the world, and its planned closing is one of the reasons why the price of the pink diamonds is rising.
In the year 2018, the revenues of Rio Tinto from the Argyle Diamond Mine amounted to about 259 million dollars, which is an increase of 26% compared to 2017.
The improvement in the revenues derives from the increase in the sales, from the improvement in the economy of the USA, and from the increase of the prices of the Company's famous pink diamonds.
The last tender of pink diamonds of the Argyle Diamond Mine, which was held on November 28th 2018, achieved record results that reflect the intensity of the global demand for colorful fancy diamonds. This tender included 63 diamonds in the colors of pink and red.
Rio Tinto also presented recently the diamonds from the Argyle Diamond Mine that will be auctioned in the tender of the year 2019- 64 extraordinary diamonds that their total weight is 56.28 carats.
Rio Tinto told that in the last 18 years, the price of the pink diamonds from the Argyle Diamond Mine that were sold in tenders rose by more than 400%.