Is it accurate to say "algunas de mis amigos" when the friends in "some" are all female out of all of my friends, which include both females and males?

If you want to say "some of my friends are girls" then: Algunos de mis amigos son chicas.

We always use feminine pronouns (pronombres femeninos) for feminine nouns (sustanitvos femeninos). 

You have to say "algunas de mis amigas" 
It depends on what you want to say...
If its to indicate something they do then say: "de todos mis amigos, algunas de las chicas [add verb here]. Meaning: From all my friends, some of the girls [verb]. 
If you need more help, don't be afraid to ask me! ^^ Spanish is my native language

~Hope this helps~ ^-^