From casual observation, the covers posted so far are generally philatelic in nature.
Here are some which originated from Antarctica. All were from individual on a team of scientists from Texas Tech College (now University), primarily Geologists, who were on one or more trips to Antarctica during the 1960s.
The first is a Christmas card mailed Dec 15, 1966.
The envelope front:
And the card outside front and back:
The sender of this card was Vestal "Pappy" Yates, and information about him can be found at this link: https://today.ttu.edu/posts/2018/03/antarctica/
The next card is from a personal letter sent from Dr. R. W. Strandtmann to his wife, who was one of my professors in graduate school. I was picking up mail one morning as she was, and noticed the cover and asked if I might have it. She was nice enough to accommodate me, and here it is. There is no postmark date, but it should be 1966.
The last is one of the semi-official cachets prepared by members of the Texas Tech Staff. It is signed by J. R. Wilbanks and V. L. Yates, who was mentioned above.
The reverse is blank.