在撰寫『淺說南非Witwatersrand 太古金礦』一 文時，面對的困難就是沒有Witwatersrand 太古金礦的經典標本，今年4月1日一次金礦的拍賣會出現了這項標本，尷尬的是礦物公司在德國，而德國此刻正遭受冠狀病毒肺炎肆虐，敝小館很不容易得標之後，終於在7月1日收到標本。

Gold With Uraninite

Witwatersrand, Gauteng Province, South Africa

4 × 6.5 × 0.9 cm  25.00gr

An interesting and super rare specimen from the Witwatersrand gold mining area. It hosts a veinlet of black uraninite, and countless gold flakes frozen in- and outside the uraninite.

This is a spectacular sample of precambrian high-grade gold ore. The rock is from the Carbon Leader (also known as the Carbon Leader Reef & Carbon Leader Seam), a blackened, hydrocarbon-rich stromatolitic interval richly impregnated with native gold (Au) and radioactive uraninite/pitchblende (UO2). It is a paleoplacer deposit, part of an ancient alluvial fan succession.
Stratigraphy & Age: Carbon Leader Member, Main Conglomerate, lower Johannesburg Subgroup, lower Central Rand Group, Witwatersrand Supergroup, lower Neoarchean, ~2.9 billion years old (cit. jsjgeology).

Slightly radioactive due to content of U, Th and/or rare earth elements (appr. 8.0 micro Sv/h within spitting distance).

From an old gold collection which was built up in the 70's, 80's and early 90's.