Question: The Letseng diamond mine, found in the landlocked Southern African kingdom of which country, a landlocked state or landlocked country is a sovereign state entirely enclosed by land, or whose only coastlines lie on closed seas?

Context paragraphs:
Letseng diamond mine: The Letseng diamond mine, found in the landlocked Southern African kingdom of Lesotho, is owned by Gem Diamonds, Ltd. and the government of Lesotho, and at an elevation of 3,100 m (10,000 ft) it is the world's highest diamond mine.

Landlocked developing countries: Landlocked developing countries (LLDC) are developing countries that are landlocked.  The economic and other disadvantages experienced by such countries makes the majority of landlocked countries least developed countries (LDC), with inhabitants of these countries occupying the bottom billion tier of the world's population in terms of poverty.  Apart from Europe, there is not a single successful highly developed landlocked country as measured by the Human Development Index (HDI), and nine of the twelve countries with the lowest HDI scores are landlocked.  Landlocked European countries are exceptions in terms of development outcomes due to their close integration with the regional European market.  Landlocked countries that rely on transoceanic trade usually suffer a cost of trade that is double that of their maritime neighbours.  Landlocked countries experience economic growth 6% less than their non-landlocked countries, holding other variables constant.

Williamson diamond mine: The Williamson Diamond Mine (also known as the Mwadui mine) is a diamond mine 23 km northeast of Shinyanga in Tanzania; it became well known as the first significant diamond mine outside of South Africa.  The mine was established in 1940 by Dr. John Williamson, a Canadian geologist, and has been continuous operation since then, making it one of the oldest continuously operating diamond mines in the world.  Over its lifetime it has produced over 19 million carats (3,800 kg) of diamonds.  The Williamson mine, once owned by its namesake Dr. Williamson and later nationalized by the government of Tanzania.  Since February 2009 the mine is mostly owned by Petra Diamonds, with 75% ownership, the government of Tanzania owning the remaining 25%.

Letseng Airport: Letseng Airport (ICAO: FXLT) is an airstrip serving the Letseng diamond mine in Mokhotlong District, Lesotho.  The runway is at very high elevation, 10,084.8 feet.

Lac de Gras: Lac de Gras is a lake approximately 300 km north east of Yellowknife, in the Northwest Territories of Canada.  Lac de Gras was the centre of the diamond rush of the 1990s.  There are three working diamond mines in the area, Diavik Diamond Mine, Ekati Diamond Mine, and Snap Lake Diamond Mine.  It was called Ekati by aboriginal peoples.

Murowa diamond mine: The Murowa diamond mine is a diamond mine located in Mazvihwa, south central Zimbabwe, about 40 kilometres from the asbestos mining town of Zvishavane in the Midlands province.  The mine is majority owned and operated by the Rio Tinto Group, which also owns the Argyle diamond mine in Australia and part of the Diavik Diamond Mine in Canada.  The mine is a combination of open pit and underground construction; current estimates put construction costs at $61 million USD and mine reserves are 19 million tonnes of ore, with an ore grade of 0.9 carat per tonne.

Lesotho Promise: The Lesotho Promise, a 603 carat (121 g) diamond stone of exceptional colour was unearthed on 22 August 2006 at the Letseng diamond mine in the mountain kingdom of Lesotho.  Announced on 4 October 2006, it is the largest reported find this century and the 15th largest diamond ever found.  The stone is rated 'D', the top colour band for diamonds.

Victor Diamond Mine: The Victor Diamond Mine is the first Canadian diamond mine located in Ontario, and De Beers' second diamond mine in Canada (after the Snap Lake Diamond Mine).  It is located in the Northern Ontario Ring of Fire, in the James Bay Lowlands 90 km west of Attawapiskat in the remote northern part of the province.  In June 2005, the Attawapiskat First Nation voted in favour (85.5%) of ratifying the Impact Benefit Agreement (IBA).  Construction of the mine began in February 2006 which created 3200 positions; mining and operations will create around 400 permanent positions.  The Victor Mine is an open-pit mine, with a processing plant, workshops, and an airstrip located on site.  By 2013-2014 royalties collected from De Beers Victor Diamond Mine amounted to $226.  At that time De Beers was continuing to pay off its "$1 billion investment to build the mine and from now until it closes, the company expects to pay tens of millions of dollars in royalties."

Landlocked country: A landlocked state or landlocked country is a sovereign state entirely enclosed by land, or whose only coastlines lie on closed seas.  There are currently 49 such countries, including five partially recognised states.  Only two, Bolivia and Paraguay in South America, lie outside Afro-Eurasia (the Old World).

Southern African Community USA: Southern African Community USA (SACU) is a registered 501(c)3 non-profit organization that was established in 2013 in the state of Maryland to promote Southern African culture and unite the Southern African Diaspora communities in the USA.  It was co-founded by 10 leaders from various Southern African countries who worked together to build an organization that focused on Southern Africans living in the USA.  It serves to create Southern African identity and cohesion in the DC area and the wider US though advocacy work, community outreach, hosting social events and acting as a resource of information on the region.  It is the first association in the United States that was organized for the region and the first Southern African Diaspora Association in the world.  It recognizes the countries of Angola, Botswana, Democratic Republic of Congo, Lesotho, Madagascar, Malawi, Mauritius, Mozambique, Namibia, Seychelles, South Africa, Swaziland, Tanzania, Zambia and Zimbabwe as members of the Southern African community in consistency with SADC member states

Supporting paragraphs: Letseng diamond mine Landlocked country
Answer: Lesotho