In Gimp program, I want to convert all the black and white pixels to silver grey pixels that used to appear when printing from b&w film negatives

I know how to use the gimp program to convert a color image to b&w. I used the desaturate>mono mixer to adjust the rgb channels. I have also seen many objects online that were colored with a silver metallic effect. Is it possible to select and recolor all Grey tones in a photo to closely match the silver Grey tones that were produced in prints similar to the results that Photographer Ansel Adam's acheived?

The metallic effect is a physical one from the chemicals used to make the print. To emulate it in software you can only make 'light grey', which you can do by tweaking the curves.

Alternatively, you could ask your print house if they have a paper with a slight metallic sheen. Tell them why you want it.