How to place custom box or block on archive page wordpress. No plugin

I need a archive page description and image box to be placed on the header of the page. I can create the box via wordpress. But just want to show this box using. I have the following code:

add_action('woocommerce_archive_description','show_category_block');
function show_category_block() {
  if (is_product_category ('mica')) {
    echo 'MICA POWDER';
  }
}

This works to output 'String' How do output a block/box

Thanks