This if fairly easy to do, but the command required is very long.
The way you should do this, as other answers have already pointed out, is by putting CanPlaceOn tags onto the item. There's no easy way to do this once the items are already in the player's inventory, so instead you should do it for the dropped item entities with /data.
CanPlaceOn is also fairly annoying in that you need to name every single block you want to be able to place the block onto. I used the block name table from the Minecraft wiki, and wrote a script to convert the names into the right format.
Overall, the command you need to run on a fast clock is:
/data merge @e[type=Item] {Item:{tag:{CanPlaceOn:["minecraft:air","minecraft:stone","minecraft:grass","minecraft:dirt","minecraft:cobblestone","minecraft:planks","minecraft:sapling","minecraft:bedrock","minecraft:flowing_water","minecraft:water","minecraft:flowing_lava","minecraft:lava","minecraft:sand","minecraft:gravel","minecraft:gold_ore","minecraft:iron_ore","minecraft:coal_ore","minecraft:log","minecraft:leaves","minecraft:sponge","minecraft:glass","minecraft:lapis_ore","minecraft:lapis_block","minecraft:dispenser","minecraft:sandstone","minecraft:noteblock","minecraft:golden_rail","minecraft:detector_rail","minecraft:sticky_piston","minecraft:web","minecraft:tallgrass","minecraft:deadbush","minecraft:piston","minecraft:piston_head","minecraft:wool","minecraft:piston_extension","minecraft:yellow_flower","minecraft:red_flower","minecraft:brown_mushroom","minecraft:red_mushroom","minecraft:gold_block","minecraft:iron_block","minecraft:double_stone_slab","minecraft:stone_slab","minecraft:brick_block","minecraft:tnt","minecraft:bookshelf","minecraft:mossy_cobblestone","minecraft:obsidian","minecraft:torch","minecraft:fire","minecraft:mob_spawner","minecraft:oak_stairs","minecraft:chest","minecraft:redstone_wire","minecraft:diamond_ore","minecraft:diamond_block","minecraft:crafting_table","minecraft:farmland","minecraft:furnace","minecraft:lit_furnace","minecraft:standing_sign","minecraft:ladder","minecraft:rail","minecraft:stone_stairs","minecraft:wall_sign","minecraft:lever","minecraft:stone_pressure_plate","minecraft:wooden_pressure_plate","minecraft:redstone_ore","minecraft:lit_redstone_ore","minecraft:unlit_redstone_torch","minecraft:redstone_torch","minecraft:stone_button","minecraft:snow_layer","minecraft:ice","minecraft:snow","minecraft:cactus","minecraft:clay","minecraft:jukebox","minecraft:fence","minecraft:pumpkin","minecraft:netherrack","minecraft:soul_sand","minecraft:glowstone","minecraft:portal","minecraft:lit_pumpkin","minecraft:unpowered_repeater","minecraft:powered_repeater","minecraft:stained_glass","minecraft:trapdoor","minecraft:monster_egg","minecraft:stonebrick","minecraft:brown_mushroom_block","minecraft:red_mushroom_block","minecraft:iron_bars","minecraft:glass_pane","minecraft:melon_block","minecraft:pumpkin_stem","minecraft:melon_stem","minecraft:vine","minecraft:fence_gate","minecraft:brick_stairs","minecraft:stone_brick_stairs","minecraft:mycelium","minecraft:waterlily","minecraft:nether_brick","minecraft:nether_brick_fence","minecraft:nether_brick_stairs","minecraft:enchanting_table","minecraft:end_portal","minecraft:end_portal_frame","minecraft:end_stone","minecraft:dragon_egg","minecraft:redstone_lamp","minecraft:lit_redstone_lamp","minecraft:double_wooden_slab","minecraft:wooden_slab","minecraft:cocoa","minecraft:sandstone_stairs","minecraft:emerald_ore","minecraft:ender_chest","minecraft:tripwire_hook","minecraft:tripwire","minecraft:emerald_block","minecraft:spruce_stairs","minecraft:birch_stairs","minecraft:jungle_stairs","minecraft:command_block","minecraft:beacon","minecraft:cobblestone_wall","minecraft:wooden_button","minecraft:anvil","minecraft:trapped_chest","minecraft:light_weighted_pressure_plate","minecraft:heavy_weighted_pressure_plate","minecraft:unpowered_comparator","minecraft:powered_comparator","minecraft:daylight_detector","minecraft:redstone_block","minecraft:quartz_ore","minecraft:hopper","minecraft:quartz_block","minecraft:quartz_stairs","minecraft:activator_rail","minecraft:dropper","minecraft:stained_hardened_clay","minecraft:stained_glass_pane","minecraft:log2","minecraft:log2","minecraft:acacia_stairs","minecraft:dark_oak_stairs","minecraft:slime","minecraft:barrier","minecraft:iron_trapdoor","minecraft:prismarine","minecraft:sea_lantern","minecraft:hay_block","minecraft:carpet","minecraft:hardened_clay","minecraft:coal_block","minecraft:packed_ice","minecraft:double_plant","minecraft:prismarine","minecraft:barrier","minecraft:red_sandstone","minecraft:sea_lantern","minecraft:iron_trapdoor"],HideFlags:16}}}
Best Answer
Sorry, not possible. You can only set items to be able to break ALL of one block type, or NONE. It is not possible to choose only certain breakable blocks.
You can try using commands to replace the decoration block if a player tries to break it, and kill the item drops before the player can pick them up.
Or, you can consider retexturing a different block to look like iron ore and have those as the decoration blocks. Although these decoration blocks may look like iron ore, they're different blocks made to look like iron ore, and therefore won't be registered as breakable.
But those two methods are about entirely different methods for entirely different posts. Try searching online for a way to accomplish your task.