Creating an if statement for a 2d contour plot to append lowest values

this may be a very simple/dumb question because I'm new to coding but I have a 2d contour plot where there is an X and Y position and also an intensity at each position (Like a 2d plot with a colourbar representing the intensity at each point). I would like to make an if statement where all points below or above a certain intensity get picked out (with their relative X and Y positions) and added to a new list which I could plot later.

I have

peaks = []
if stack[i, j] < -1.0 or stack[i, j] > 1.0:
    peaks.append(i, j)

And i'm just stuck and have no clue where to take it from here.

Thank you!