Lapis lazuli (lazuritic gneiss) (Sar-e-Sang Deposit, Sakhi Formation, Precambrian, 2.4-2.7 Ga (?); Sar-e-Sang Mining District, Hindu-Kush Mountains, Afghanistan) 3

            Lapis lazuli (lazuritic gneiss) from the Precambrian of Afghanistan. (~7.3 centimeters across at its widest)

Blue = lazurite
Whitish = calcite
Brassy gold specks = pyrite (click on the photo to zoom in and see these)

Lapis lazuli is one of the most gorgeous rocks I’ve ever seen.  The highest quality lapis lazuli in the world is from northeastern Afghanistan (northern Kuran Wa Munjan District, southern Badakhshan Province).  Lapis lazuli is both Latin & Persian for “heaven stone”, or “sky stone”, or “blue stone”.  This rare rock is dominated by the deep-blue mineral lazurite, which is a sodalite-group feldspathoid - (Na,Ca)8(AlSiO4)6(SO4,S,Cl)2.  Commonly, whitish streaks of calcite (CaCO3) and brass-colored specks of pyrite (FeS2) are present.  Lazurite is essentially the most intensely-blue mineral known (azurite is also consistently intense blue).  The intensity of the blue color in lazurite has been attributed to the sulfur and calcium content.
 
Lapis lazuli is known from elsewhere in the world, but northeastern Afghanistan is the classic locality.  Afghani material has been reportedly mined for at least 7000 years.  In ancient times, lapis lazuli was referred to as “sapphire”.  Pliny the Elder's 37-volume work Naturalis Historiae, or Natural History, written in about the 70s A.D., refers to Afghani lapis lazuli as “sappiri”, and notes that it has glistening dots of gold in it - see his book 37.
 
Afghani lapis lazuli comes from the Sar-e-Sang Deposit, which consists of ~1-8 meter thick and ~20-450 meter long, north-south trending veins, lenses, and layers of lapis lazuli hosted in high-grade marbles.  Stratigraphically, this is the marble member of the Sakhi Formation, Anglich Group, Sar-e-Sang Series.  This material is Late Archean to early Paleoproterozoic in age (?) (2.4 to 2.7 billion year metamorphic dates come from Pamir in adjacent Tajikhistan).  The lapis lazuli rocks appear to be the result of retrograde metamorphism and/or metasomatism (alaskite granite & pegmatite & basic dike intrusions are nearby).  They occur along the eastern limb of the Kokcha Anticline, and are part of the Fayzabad Metamorphic Massif in the South Badakhshan Block.

The lapis lazuli mines of northeastern Afghanistan are some of the most difficult-to-access localities in the world, occurring along steep slopes of deeply carved, narrow river canyons in the northern flanks of the western Hindu-Kush Mountains.  The Sar-e-Sang Mining District (apparently synonymous with “Firgamu Mines”) occurs about 1500 feet above river water level.  The mines are above the lowermost reaches of the Sar-e-Sang River, a west-flowing tributary of the Kokcha River.  This stretch of the Kokcha River is quite isolated.  The nearest villages are Koran-o-Munjan (to the south) and Robat-e-Payan (to the north).  Fayzabad, the nearest sizable town, is about 100 km to the north-northwest of the Sar-e-Sang Mines.

Location of Sar-e-Sang Mine adits: approximately 36° 12.2’ to 36° 14.14’ North latitude, 70° 47.85’ to 70° 48.63’ East longitude.
 
Access to the Sar-e-Sang Mines is only via narrow foot trails in a barren, but harshly beautiful landscape.  Regarding this area, British Army Lieutenant John Wood famously said in 1837: “If you do not wish to die, avoid the Valley of Kokcha.”

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Taken on: April 12, 2019

Tags:

lapis

lazuli

Sar-e-Sang

Deposit

Sakhi

Formation

Precambrian

lazurite

calcite

pyrite « less

Sets appears in: • Blue Rocks & Minerals • Lapis Lazuli

Groups appears in: • Earth Science Teaching Resource • in explore more » • 6,000 Views Unlimited 6000 • Perspective 2019 « less

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